Lead acid or agm/gel

[smac999]

600w load is a decent load on a 200ah bank. Even brand new batteries will struggle. That would last under 2 hours on brand new batteries.

To run your 3000w inverter you’d need atlesst 800ah

[waterman46]

Of course both AGM and flooded cells are actually both lead-acid. Now that's out of the way, I think the selection should be based at least greatly on your intended use. Either type can give good performance and lifetime if properly cared for.

For me, AGM is an obvious best choice. I want no chance of acid spill. And I want to have no worries about topping up the electrolyte or any desire to measure the pH.

I leave the boat for extended periods in the care of a three-stage battery charger with only the automatic bilge pumps turned on. If I had floating cell I would worry about depletion of electrolyte, which can ruin a battery very quickly.

The cheapest option is floating cell in form of golf cart batteries. If you are on the boat at least once a month with time and inclination to check the electrolyte or install and maintain a reliable auto watering system, and don't worry about venting the hydrogen or spilling the acid, then go for floating cell golf cart type.


If you change the existing type or size of battery, you will have to modify your battery mounting configuration, which can be a major choice-maker also.

[Gaia]

Originally Posted by noelex 77

Propane/butane is not the ideal fuel on a boat, so I can understand the desire to move over to electric cooking. Personally, we only use propane/butane for a small percentage of cooking. However, you need to understand that electric cooking uses lots of power and this power needs to be produced.

If you are planning to be away from shore power for a reasonable percentage of the time, 350w of solar combined with a small wind generator and 200 AHr of battery capacity is not enough to consistently sustain electric cooking together with the other house demands.

You are likely to need significant run times on the petrol generator. I don’t think this is an improvement over the traditional propane/butane arrangement . In fact, with the drawbacks of a petrol generator such as noise etc it is a significant step backwards.

Electric cooking is great, but you need a large solar array and battery bank (or a marine diesel generator) to make this viable.

Anyway, good luck with whatever you decide, but at least consider retaining the propane/butane system (if it is not too late). Camping gaz bottles are too small for full time cruising so you need a system that uses much larger bottles.

If you are unsure consider a combination of electric and propane/Butane cooking depending on the available electrical power available. This reduces the biggest frustration of propane, which is arranging replacement bottles in a world that has no universal standards.

In our experience during a 25 yr living on board and a 23 yr long circumnavigation we have found buying propane at the very most a minor frustration. But experiences differ. Right now in the Rio Dulce propane is 100m away by dolly😊

We have 8 100 ahr 12v AGMs and about 800 w of solar. Half of these panels are more than 20 yrs old. Our last set of batteries were Japanese Yuasa bought in Singapore for around 100 $ each.and they were replaced in Florida a couple of years ago after 8yrs of trouble free use. They were still doing the job but gave hints of possible demise and as we were headed for a season in the Bahamas we replaced them with Vietnamese built AGMs that appeared identical to the Yuasas. If I remember correctly they were about 120 or 140$ each. They like the Yuasas seem to be good batteries. We bought then through Walmart.

We are now in Guatamala at a dock and have been here for almost two months. We are not hooked up to power at the dock. We have a 1500 or 2000w inverter. It has been there for so many years I cannot remember. It operates all our power tools with the exception of a Bosch multi tool which does not seem to like the shape of the sine wave put out . I am guessing. LED lights of course. Particularly useful as navigation lights when under way.

We are doing a lot of maintenance on the steel boat and as we are in isolation and under a curfew we have gotten into a movie watching habit at night so our power consumption is higher than normal. We normally keep up during the day but sometimes drop down to 70 or 80Ah by sunrise particularly if it has been more cloudy during the day and hotter than normal. 40 deg calls for many fans. Major consumption are the many fans, power tools and computers and sometimes two fridges. No freezer. We cook with gas as mentioned.

We seldom use the engine for charging while underway. We use a Raytheon 7002 autopilot. It, computers and the fridge are the main power users under way.

We also have a mast top mounted wind generator but it seems only of use when sailing with the wind forward of the beam or of course when the apparent wind is over 20 knots.

I would not even consider having a generator on board. The noise would irritate too much. Having a gasoline powered outboard is bad enough but our trial with a Torqeedo was a disaster.

Hope this real world experience is of help.

Jim sv GAIA

[SJFK]

Recommend you read Nigel Calder’s account of his Firefly batteries. Power is everything when you are on passage, and your auto helm can draw lots of power and if you use radar especially at night then you need lots of power. A hydro generator is very effective but expensive, and only good when the propeller is turning. The best wind turbine is the D400 but it is pricy. But fills the gap when it is breezy and overcast which means your solar will not generate as much as you expect. If it is overcast and no wind then a small generator will be much cheaper to run than your main engine, though look at capital costs to see what your break even point will be, and consider the noise you will make if lying close to other yachts. Yachting is all about compromise, and the more money you have the less you have to compromise.
Good luck

[Pelican 2]

I had 230AH of lead acid when I bought my current boat 4 - 5 years ago. They were 6V golf cart deep cycle batteries in series. The ones that came with the boat lasted 3 months but with weekends away (just two days) and only sailing they would regulary drop below 12V and hit 10.2V alarms at times. I replaced like for like with new batteries. They died in less than a year. I next replaced with the same batteries but increased the quantity to 6 6V deep cycle 230AH batteries and swapped the solar / wind controller to MPPT from the original unit. I added one more 300W solar rigid panel so I have 600W solar and 600W wind turbine. When sailing the wind turbine works hard but at anchor does not do that much normally. It is a high wind model just 3 blades. However now, completely off grid, my batteries hover from 12.2v to 14.3v and occasionally, when i an away for a week or more, i need the assistance of the engine alternator to boost things a bit. The electric toaster and microwave are the only items that pull the bank below 12V but only to 11.8V minimum. I used to fill the batteries every week with the 230AH bank. Now it is less than once in two years. They have been installed 3 years. My battery tester still checks the bank as 86% good.

[Pelican 2]

That is to say 690AH at 12V

[Gaia]

Originally Posted by Pelican 2

That is to say 690AH at 12V

It is of course stating the obvious but the way to save money on batteries is to have more of them. Our 800+AH bank is seldom drawn down to even 12.4v. 12.5 or even 12.6 at the end of the night is more the norm. If it was we would add more solar and more batteries.

And the other comments, on Radar, broadband sips power and we now leave it on all night while our Raytheon AP with the latest controller and with GAIA as balanced as we can get her also draws little when we lower the response so that the rudder moves just a little as we sail along.

But then we lack electric toasters and a microwave instead rely on propane and gasoline for the outboard as earlier discussed by others. Unfortunately those fossil fuels pack a wallop of energy for their weight.

Whatever works

Jim sv GAIA

[Pizzazz]

F жззззДзобйзлЬйжзу

[ranger58sb]

Originally Posted by Culwatty

So currently have numax dual purpose batteries 200ah house and 100ah for the starter.

My main thoughts are that a good agm claims to have
600 cycles @50% DOD £259
Vs
lead acid 100 cycles @50% DOD £120

Both 120ah with a good discharge rates

Don't know your market area, but you could maybe shop some more. And that 100-cycle flooded battery sounds like a starting battery, not dual-purpose, certainly not deep cycle.

There are AGMs spec'd at 1000 cycles to 50% DoD (see Lifeline, maybe others). See also Firefly Carbon Foam AGMs, said to permit 80& DoD and decent recovery even after extended "partial state of charge" (PSOC) operation. There are also flooded batteries, usually 6V golf cart batteries, aka BCI Group GC2, spec'd to 1000 cycles (see Trojan T-105s and others).

If you mean your house batteries are 2x 100-Ah (maybe Group 31s?) then you might look specifically at replacing with 2x GC2s for ~220-Ah total, and you might find you can fit 4x (~440-Ah) into only a slightly larger space.

Once you've chosen form factor, you can choose AGM or flooded. Former offers some advantages not related to cycles, latter is less expensive.

-Chris

[Culwatty]

Originally Posted by kas_1611

Maybe I'm missing something but why the extra generator(s)? You have a large diesel engine with a big alternator, isn't that enough generation?


Why not invest in a much larger house bank, say at least 4x 120amp-hr batteries in parallel to give you almost 500amp-hrs (OK 250amp-hrs at 50% DOD) and more solar capacity. I have seen 200amp-hr L/A or AGM batteries available which would increase your storage capacity without overly increasing the footprint.

That would get rid of the need to carry extra petroleum for the generator, reducing the explosion and fire risks.

if you can afford AGM then go with them as they can withstand much higher heel angles, last a long time, can be discharged slightly deeper than their L/A cousins and you don't need any fancy charge controllers as most will adjust easily.

Hi!

So yes the alternator does a good job of topping the batteries up, I think its a 70A but with the sterling charge controller

Something else I realised is my hot water system either heats from the engine coolant or 240v so for a hot shower every so often I would prefer to run the generator, charging batteries and producing hot water and cooking a proper dinner at once... was my thoughts anyway!

The larger house bank is going to happen its more of the to go for agm or not...

My solar charge controllers are crapping out on me anyway so I will be purchasing new ones, alternator has the switches to go agm. 240v charger I need to check. Same as the Rutland will see if I can change to agm or need a new controller 🤔

Thanks for the input its all being written down in pros and cons!

Originally Posted by Captain Puget

2 thoughts -

- the carbon foam / Firefly batteries very simple and forgiving. Going on 4 years and no problems.

- reduce fuel diversity. I’ve chosen to cook and heat with diesel (except for barbecue), with a single gas hot plate for backup (the little high arising can type). Also I’ve moved to electric for the dingy motor. No gasoline onboard, less flammability and carbon monoxide risk.

Nice i have just been looking at electric outboards. Going for a 68lb thruster as its just me and supplies

Are you using a wallas diesel Cook top?

I'm much rather use all diesel but struggling to find the combination without spending mega bucks. Where as 240v hob is £34 by tefal here so carrying a spare isn't an issue

Definitely like the idea of reducing fuel diversity!

Originally Posted by noelex 77

Propane/butane is not the ideal fuel on a boat, so I can understand the desire to move over to electric cooking. Personally, we only use propane/butane for a small percentage of cooking. However, you need to understand that electric cooking uses lots of power and this power needs to be produced.

If you are planning to be away from shore power for a reasonable percentage of the time, 350w of solar combined with a small wind generator and 200 AHr of battery capacity is not enough to consistently sustain electric cooking together with the other house demands.

You are likely to need significant run times on the petrol generator. I don’t think this is an improvement over the traditional propane/butane arrangement . In fact, with the drawbacks of a petrol generator such as noise etc it is a significant step backwards.

Electric cooking is great, but you need a large solar array and battery bank (or a marine diesel generator) to make this viable.

Anyway, good luck with whatever you decide, but at least consider retaining the propane/butane system (if it is not too late). Camping gaz bottles are too small for full time cruising so you need a system that uses much larger bottles.

If you are unsure consider a combination of electric and propane/Butane cooking depending on the available electrical power available. This reduces the biggest frustration of propane, which is arranging replacement bottles in a world that has no universal standards.

Yes totally agree the current setup needs revamping, looking across so far I'm thinking that electric with my jet oil as a backup as I already have loads of fuel for that!

My main reason for keeping the generator is welding work. But I'm starting to wonder if I need to find a diesel generator and marinise/silence it in its own sealed box with an overboard vent

Thank you for your input also

Originally Posted by MJH

Keep it simple...start from the beginning. Complete an electrical use survey to see what your daily electrical needs are. See where you can reduce your electrical needs thereby reducing battery size. Select the battery chemistry for your lifestyle that you will maintain properly...go for the long term cost/amp. Use more solar to maintain them. Forget the generators, induction cooktop, and electric oven...use propane.

~ ~ _/) ~ ~ MJH

This is the hard part, doing the electrical survey right now I use next to no power, charge my tablet and phone, few led lights, and the vacuum, cooking is done with the gas, mostly tinned soups and coffee.. oven doesn't work and needs an overhaul as well as a "proper" gas alarm fitted to pass safety certificate.. that on its own will cost more than oven hob and almost an extra battery... I do hear what you are saying, used to run a George forman grill from my land-rover for lunch and I only had 330ah then! 😅😅

Power usage will go up when I'm actually on the move, autohelm lights etc

Unfortunately I will need a generator one way or another as I would not want to risk welding from the inverter!

Originally Posted by MAJICDAN

100 cycles led acid??? That is only three months!!!
600 cycles AGM??? That is less than two years.
I have two house battery banks of 10 size 31agm deep cycles and 10 golf cart batteries because of their size.
I have used cheap Sams golf cart batteries for the last five years and am just thinking about replacing them.
I am on my second and third set of AGMs
The golf cart batteries cost 1/3 of AGM and have lasted over twice as long.
Plus the AGM would suddenly go bad
I had three AGM failures in the last six months while in the Virgin Islands
The golf cart batteries all still work but have all diminished equally
To start with you will need twice as many batteries as you think so you do not drain them down so low.
AGMs you can not easily test.
I take the temperature of each AGM each month.
I test the specific gravity of each golf cart battery cell every month and fill them with distilled water.

Have you had the agm batteries tested to see why they failed?

Yes I wish I could spend the money for lithium, but right now its just not going to happen 😔

Golf cart batteries get another vote!

Originally Posted by Starbuck

The OP, he say:


Culwatty, The Trojan T-105 is a 6-volt, deep-cycle, flooded lead acid battery that many in the cruising community promote as, arguably, the standard to compare all others by. Two are wired in series to create a 12-volt battery; two or more of these pairs are then wired together in parallel to achieve the desired house bank capacity, in terms of amp-hours.

Ah thank you for that explanation!

Originally Posted by waterman46

Of course both AGM and flooded cells are actually both lead-acid. Now that's out of the way, I think the selection should be based at least greatly on your intended use. Either type can give good performance and lifetime if properly cared for.

For me, AGM is an obvious best choice. I want no chance of acid spill. And I want to have no worries about topping up the electrolyte or any desire to measure the pH.

I leave the boat for extended periods in the care of a three-stage battery charger with only the automatic bilge pumps turned on. If I had floating cell I would worry about depletion of electrolyte, which can ruin a battery very quickly.

The cheapest option is floating cell in form of golf cart batteries. If you are on the boat at least once a month with time and inclination to check the electrolyte or install and maintain a reliable auto watering system, and don't worry about venting the hydrogen or spilling the acid, then go for floating cell golf cart type.


If you change the existing type or size of battery, you will have to modify your battery mounting configuration, which can be a major choice-maker also.

I think this has just made my mind up as far as wet cells, the point the batteries are going to be mounted it will be a horrible job to check and maintain levels. At least agm can be mounted on the side, giving me a larger space to fit them and therefore a bigger bank.

Originally Posted by Gaia

In our experience during a 25 yr living on board and a 23 yr long circumnavigation we have found buying propane at the very most a minor frustration. But experiences differ. Right now in the Rio Dulce propane is 100m away by dolly😊

We have 8 100 ahr 12v AGMs and about 800 w of solar. Half of these panels are more than 20 yrs old. Our last set of batteries were Japanese Yuasa bought in Singapore for around 100 $ each.and they were replaced in Florida a couple of years ago after 8yrs of trouble free use. They were still doing the job but gave hints of possible demise and as we were headed for a season in the Bahamas we replaced them with Vietnamese built AGMs that appeared identical to the Yuasas. If I remember correctly they were about 120 or 140$ each. They like the Yuasas seem to be good batteries. We bought then through Walmart.

We are now in Guatamala at a dock and have been here for almost two months. We are not hooked up to power at the dock. We have a 1500 or 2000w inverter. It has been there for so many years I cannot remember. It operates all our power tools with the exception of a Bosch multi tool which does not seem to like the shape of the sine wave put out . I am guessing. LED lights of course. Particularly useful as navigation lights when under way.

We are doing a lot of maintenance on the steel boat and as we are in isolation and under a curfew we have gotten into a movie watching habit at night so our power consumption is higher than normal. We normally keep up during the day but sometimes drop down to 70 or 80Ah by sunrise particularly if it has been more cloudy during the day and hotter than normal. 40 deg calls for many fans. Major consumption are the many fans, power tools and computers and sometimes two fridges. No freezer. We cook with gas as mentioned.

We seldom use the engine for charging while underway. We use a Raytheon 7002 autopilot. It, computers and the fridge are the main power users under way.

We also have a mast top mounted wind generator but it seems only of use when sailing with the wind forward of the beam or of course when the apparent wind is over 20 knots.

I would not even consider having a generator on board. The noise would irritate too much. Having a gasoline powered outboard is bad enough but our trial with a Torqeedo was a disaster.

Hope this real world experience is of help.

Jim sv GAIA

Hi Jim!

You are living my dream!

Do you run a welder on board? When you say down to 80ah do you mean you have used 740ah from the bank?

I'm curious about your disaster with the torqeedo? I'm hovering over a 68lb thrusters buy button as we speak!

That is helpful thank you! Plan today to start repairing the Rutland support as its been cross threaded....

Originally Posted by SJFK

Recommend you read Nigel Calder’s account of his Firefly batteries. Power is everything when you are on passage, and your auto helm can draw lots of power and if you use radar especially at night then you need lots of power. A hydro generator is very effective but expensive, and only good when the propeller is turning. The best wind turbine is the D400 but it is pricy. But fills the gap when it is breezy and overcast which means your solar will not generate as much as you expect. If it is overcast and no wind then a small generator will be much cheaper to run than your main engine, though look at capital costs to see what your break even point will be, and consider the noise you will make if lying close to other yachts. Yachting is all about compromise, and the more money you have the less you have to compromise.
Good luck

Hi!

Yes generator is mainly for welding work and hopefully seldom top ups!

I have seen a successful diy waterturbine generator, using an alternator and a long braided rope with a prop on the end! With things like that I would rather make than buy 😁😁

Will look up nigel Calder 👌

Yes I'm also looking into building a wind windvane self steering mechanism, but that's a few months off yet!

Originally Posted by Pelican 2

I had 230AH of lead acid when I bought my current boat 4 - 5 years ago. They were 6V golf cart deep cycle batteries in series. The ones that came with the boat lasted 3 months but with weekends away (just two days) and only sailing they would regulary drop below 12V and hit 10.2V alarms at times. I replaced like for like with new batteries. They died in less than a year. I next replaced with the same batteries but increased the quantity to 6 6V deep cycle 230AH batteries and swapped the solar / wind controller to MPPT from the original unit. I added one more 300W solar rigid panel so I have 600W solar and 600W wind turbine. When sailing the wind turbine works hard but at anchor does not do that much normally. It is a high wind model just 3 blades. However now, completely off grid, my batteries hover from 12.2v to 14.3v and occasionally, when i an away for a week or more, i need the assistance of the engine alternator to boost things a bit. The electric toaster and microwave are the only items that pull the bank below 12V but only to 11.8V minimum. I used to fill the batteries every week with the 230AH bank. Now it is less than once in two years. They have been installed 3 years. My battery tester still checks the bank as 86% good.

Brilliant! Thanks for the useful information haha I had not considered a toaster!

Originally Posted by Gaia

It is of course stating the obvious but the way to save money on batteries is to have more of them. Our 800+AH bank is seldom drawn down to even 12.4v. 12.5 or even 12.6 at the end of the night is more the norm. If it was we would add more solar and more batteries.

And the other comments, on Radar, broadband sips power and we now leave it on all night while our Raytheon AP with the latest controller and with GAIA as balanced as we can get her also draws little when we lower the response so that the rudder moves just a little as we sail along.

But then we lack electric toasters and a microwave instead rely on propane and gasoline for the outboard as earlier discussed by others. Unfortunately those fossil fuels pack a wallop of energy for their weight.

Whatever works

Jim sv GAIA

Yes I totally agree wallop for the weight is in fossil fuels favor! I'm going to have to spend the money on the batteries, agm for sure now!

Originally Posted by ranger42c

Don't know your market area, but you could maybe shop some more. And that 100-cycle flooded battery sounds like a starting battery, not dual-purpose, certainly not deep cycle.

There are AGMs spec'd at 1000 cycles to 50% DoD (see Lifeline, maybe others). See also Firefly Carbon Foam AGMs, said to permit 80& DoD and decent recovery even after extended "partial state of charge" (PSOC) operation. There are also flooded batteries, usually 6V golf cart batteries, aka BCI Group GC2, spec'd to 1000 cycles (see Trojan T-105s and others).

If you mean your house batteries are 2x 100-Ah (maybe Group 31s?) then you might look specifically at replacing with 2x GC2s for ~220-Ah total, and you might find you can fit 4x (~440-Ah) into only a slightly larger space.

Once you've chosen form factor, you can choose AGM or flooded. Former offers some advantages not related to cycles, latter is less expensive.

-Chris

Thanks Chris, yes I see what you are saying, I am in the UK Dartmouth to be exact, currently alpha battries have been the best as far as detailed spec and prices, but happy to learn of more websites!



Thanks again everyone for sharing your experiences, its really helpful!

[Culwatty]

Originally Posted by smac999

600w load is a decent load on a 200ah bank. Even brand new batteries will struggle. That would last under 2 hours on brand new batteries.

To run your 3000w inverter you’d need atlesst 800ah

Yes I do agree, I used to run that same 600w from 330ah bank and it was doable but not ideal, I know I have an upgrade coming soon!

[SV THIRD DAY]

If you can't afford LiFePO4 yet....then FLA is the way to go.

Crunch the numbers!!!

Originally Posted by SV THIRD DAY

I think it's been close to 5years since I installed my 400AH Prismatic cells
(4-3.2v 400AH cells). I can report back now that not only is LEAD DEAD...but once you make the change to LiFePO4 batteries it's a complete game changer for full time live aboard cruising. I think that's almost a universal feeling I get when I talk to other early adapters of the technology. My original install was dead bones simple. Cell monitoring with a cell log and then I simply set all of my charging devices to 13.4 initially then over the years bumped it up to 13.6v. Being a full time liveaboard I never risked long periods of 100% SOC or overcharging due to the lower voltage charge set-point. For safety I had a low voltage buzzer...no cut off (full timer aboard remember). Original cost installed for the system: $2400.

The original set-up is still going great, but it's time for an upgrade and HOLY Smokes has the technology matured and come down in Cost. At today's cost the only thing keeping every cruiser from switching to LiFePO4 batteries is the initial upfront cost, because in the long run, LiFePO4 is now simply cheaper than Lead. Folks on this thread probably don’t need to hear that, but I remember all the slings and arrows from the naysayers back in the early days.

I'm about to pull the trigger on the following:
16qty 3.2v 280AH aluminum cased prismatic cells at $82.67ea
So total battery bank capacity will be 1120AH. (usable 10% to 90%, or 80% of capacity = 896AH)
Total Cell cost will be $1322.72
Shipping China to San Diego will cost $512
So my batteries with terminal buss bars included cost will be $1834.72.
I will add a BMS to each of the 4-280AH 12v battery banks at $80ea (with Blue Tooth)
So for the battery with BMS I will be paying landed in San Diego, $2154.72
The cost per Usable Amp Hours is $2154.72/896 = $2.40

Now some easy math, my first 400AH LiFePO4 bank 5yrs ago with NO controls/BMS cost me $7.5/Amp Hour for the usable AH. ($2400/320AH). Fast forward 5yrs and now my NEW Bank today will cost me $2.40/Amp Hour. ($2154.72/896AH).

Now let’s do some easy math of a Lead Acid Comparison. Just because it’s fun for the new folks who still think LiFePO4 batteries are too expansive. Being Generous, to buy usable amp hours of 896, you would need to double that to 1792AH of lead. (yes we all know you really have less than that…but lets do a lead best case). You can buy a 225AH Lifeline AGM GPL-8DL off Amazon for $770. https://www.amazon.com/Marine-Lifeli.../dp/B0029XJ1UQ
So you will need 8 of the lifeline AGM GLP-8DL batteries at $770ea so a total cost of $6,160. Your Cost per usable Amp Hour turns into $6.87!!! That’s just economics, not counting the space, weight, and other benefits of LiFePO4 Batteries.

Ok ok…ok….you are cheap and say you can buy Costco wet lead acids for less and my numbers are skewed for Lifeline AGMs. Ok, lets play that game next. You go to Costco and get your free lunch samples and still using the generous 50% usable rating from your Costco batteries you would need 14 of the $89 batteries to give you the same usable 896AH, maybe you can put them in your Keel for ballast? So that would cost you $1246…plus tax and battery core charges…�� https://www.costco.com/Interstate-27...100476408.html

So looking at the Costco Batteries you are paying $1.39 per usable Amp Hour ($1246/896AH) vs the LiFePO4 of $2.40, but you did get a free lunch and some new ballast for your boat. But that fee lunch doesn’t sound so hot when you will have to replace those 14 costco batteries 4-5 times during the lifespan of the same LiFePO4 battery bank….how much did you save again?

[MicHughV]

hands down..like others have mentioned here...is the 6v battery golf cart type....two of them wired together to make 12v..the only significant difference between a 6v and a standard 12v battery is that the 6v battery stands a little higher than the 12v battery and could pose a problem wherever your batteries are located, but if that is addressed, 6v is the way to go and remain within budget. Shop for the 6v battery at a battery or golf cart outlet and not West Marine as they will be easily half the price coming from West Marine.

[argonauta1]

Agree with Starbuck. Had same setup Trojan T105s times four @ 440 Amphours at 12V plus on a separate bank, two 12 V gels @ 360 Amphours or 800 total. plus the usual high capacity start battery. Gels were less reliable/shorter lasting than the Trojans. Yes, cook with propane. Yes, the obvious question: how about charging?: one 300 amphour alternator plus a 120. Diesel: Yanmar 55 hp 4 CYL normally aspirated. Also a wind gen and 2 solar panels.

[The Sun King]

My first two boats, Knightmare and Sun King both used FLA batteries and performed well. I am presently evaluating AGM for Gopher II and Sunflower in a static system powering my house. I have seen new AGMs ruined in short order and I have seen used ones last more than a decade. The key is how you treat them.


You cannot charge them too quickly and they are fussy about voltages. AGMs that have died young from overcharging CAN sometimes be brought back with some effort. In the specific case of the ones I saw ruined, there were 3 strings of 100ah batteries on a 10kw solar array in a 48v system. That's about a 200 amp charging current, way above what is recommended for those particular batteries.


For the new boats, there were design complications in dealing with hydrogen, so I decided to just avoid the issue by going to AGM.


Bear in mind that all four of these boats are electric boats, Sun King, Gopher and Sunflower being solar powered. Batteries are absolutely critical. One design rule in my boats is that they must be able to cruise all night and still have capacity to run the coffeemaker and microwave in the galley at any time. Another is to be able to cruise on cloudy days. Sun King dealt with 4 straight days of clouds, though at reduced speed by the fourth. It is important to not overdischarge either type of battery if you wish them to live long lives. More than 50% discharge is asking for trouble, so having enough battery is important in setting up your power bank.


FLAs are much cheaper and very tolerant of high charge rates, as long as you keep the water levels up. Can you carry or find sufficient distilled water? Are you going to maintain the watering? Can you ventilate the hydrogen and acid fumes?



AGMs can have long life and offer spectacular discharge rates, but require careful charging. They cost a lot more, but you don't have to water them or worry about fumes.


Carefully evaluate how much battery you need, then double it. Carefully assess how you will be charging them, too. An alternator can be death to a small battery bank.