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Old 16-07-2020, 21:43   #16
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Re: Best batteries for $2k budget

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We are refitting our 45 foot cutter and have recently removed 8 x old Trojan t105 225 AH 6v batteries from the boat so that we can replace them with brand new batteries before we set off on an indefinite ocean voyage (Pacific crossing etc).

With a budget of around $2k for the batteries i am trying to decide what the best bang for my buck would be.

we use about 250 amps/day, will have a solar array of 800 watts and a honda generator running an 80 amp charger as backup. smaller 65 amp alternator on the engine. may add a wind generator.

We are considering an induction cooktop but not sure if it is possible within our battery budget, but if it isn't, we will scrap that idea.

We will be living on anchor ALL the time and therefore will be trying to make the system as independent from the generator as possible.

Options i am considering right now are:

8 x trojan t105 for a 900AH bank @ $1500 (can it handle the high loads of induction cooktop without damage??)

6 x Northstar blue+ (carbon enhanced) 100Ah for a 600AH bank @ $1680

4 x firefly (carbonfoam) G31 for a 460AH bank @ $2280
Money no object I would go for the Fireflies, 8-10 of them. Alas, 4 is not really a big enough bank for your amount of usage.4

I have 2 Trojans on my boat (20' boat so getting 2 onboard was a trick.
Trojan has a good rep, I don't know about Northstar.
You can be pretty confident the Trojans are really deep cycle.
900Ahr is a good sized bank for your situation.

You can expect to average about 270Ahr/d out of 800w of panels.
What happens when you have cloudy days. Let's say output drops to 100Ahr/d. That means if you continue to draw 250Ahr/d then you will need to run the generator on the 4th day in order to not go below 50%SoC.

With a 600Ahr bank You would need to start the generator on the 2nd or 3rd cloudy day.

The Fireflys are different in that you expect to go to 80%DoD but that still means you need to start the generator on the 2nd cloudy day with the 400Ahr bank..

Going with the Trojans also puts you in a better position to consider converting to an electric cooking. For cooking you can expect to use 50-150Ahr/d depending on your cooking habits. I worked up a chart to estimate daily electrical cooking usage depending on how much propane you are currently using. How long does a tank last you and how many lb or kg is it?

The reason the bigger bank is better for cooking is that when you are cooking there are typically very high loads for fairly short times. A larger bank deals with that better regardless of how much total energy is withdrawn, the large instantaneous load is spread over more batteries.

If I was going to go to electric cooking I would add another 200-400W of panels or find a way to decrease my average draw for other uses.

What Honda generator do you have? The 2200I is rated for 1800W continuous which is about 150amps at 12v. If you are discharged to 50% even FLAs such as the Trojans will happily accept 0.1C or so, call it 90-100amps.
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Old 17-07-2020, 05:04   #17
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Best batteries for $2k budget

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we use about 250 amp HOURS per day,


There, fixed it for you. Saves StuM from having to do it.
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Old 17-07-2020, 05:34   #18
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Re: Best batteries for $2k budget

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8 fireflys. it will give you the AH you are taking out.

460ah is not going to cut it with 250ah a day of use unless you have sun every day.

800+ ah alows you to have a rainy day or 2.
It is if you understand Firefly batteries

Plus you don't normally take the 250AH out of the battery, that is just how much you use in a day.
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Old 17-07-2020, 06:33   #19
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Re: Best batteries for $2k budget

First question is what is the time frame your using the 250 AH, is it in a 24 hr period?
If so then 400 AH or so ought to be enough, because we can assume 1/2 of that or so between charge cycles.
The problem is the budget.
Forget LFP, that’s a fantasy on $2K.
Firefly is $5 an AH.
Good flooded can be had for $1 an AH.

I’m going to Firefly this year as well. I’m going with three L16’s which will give me 450 AH, but they cost more than $2,000. We use 150 AH between charge cycles, I have no idea of total usage. But if we go to bed with them close to 100% then we will discharge them only to 75% SOC, before next charge cycle. If it looks to be a bad Solar day, I’m not shy about running the Honda.

Those that want to or are running large as in many batteries connected in parallel ought to do some research into paralleling batteries and it’s effect on charging and drift in charge, and equalize often.

With a budget of $2,000 I would go with flooded golf cart batteries, lots of them. That would give me as many AH as will fit and it’s likely they can be found in the wild, it’s not likely that Fireflies can be.

Fireflies seem to be only a US thing as in it seems to be the only market, and even there all them are imported by one company? The Fireflies company history is “interesting”. I believe it has gone bust twice so far? I wonder how deep it’s market penetration actually is and how much actual sales there are?
I’m going to try them, but I don’t think I would for a circumnavigation, I think I’d want something that’s more available and tried and true, even if it’s not the latest tech.

Now before people start saying I’m bashing them, I’m not, but it’s one thing to be sitting in Fl cussing your batteries, and another to be doing so in the wilds somewhere
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Old 17-07-2020, 10:02   #20
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Re: Best batteries for $2k budget

At 250a\hr per day I would want to be somewhere close to a 1000a/hr bank - 48hr to 50% or 1 week in 'emergency mode'. Simple reasoning, electrical systems can and do fail for lots of reasons. Sod's law says it will happen at the most inconvenient time and you don't want to have to shut down nav, fridges and have no lights while you get somewhere to fix it. I use 80-100A/hrs per day and have 400A/hr fla bank (2x6v). Just replaced them and the last ones did more than 12 years with lots of abuse.

At you budget FLA's is the way to go and anyway still represents the best value for money. For 'habour hopping' or weekend sailing sealed batteries may have advantages but not for expedition cruising. Lithium is both expensive and unnecessary unless you need very high currents (A/C, electric cooking etc) or have major problems with weight such as a super light boat or racing.

The key to good service from Fla's is the right charging setup. You MUST fit an external smart regulator and ideally an alternator setup that gives an output 20-25% of your banks A/hr so you are looking for 250a plus if possible. That is either twin alternators or a DC generator coupled to the engine. A standard alternator generally only gives about 2/3 of its rated output on fast idle or cruising speed (rated output is at 6000 alternator rpm) so a 120a alternator will give about 80a = over 3hr engine run time per day. Your solar array will give max 70a/hr on a good day typically around 50 in reasonable conditions. Useful for top up and to reduce cycle loads only.
If you do go with FLa's the key is to fit the largest possible batteries, I do mean batteries not bank. The expected cycle life for the same quality battery about double between 12v, 6v and 4v with 12v rated about 1,500 cycles and 4 volts around 4,500 cycles (Rolls batteries) my suggestion would be 3off 4KS21P from the Rolls range but there are others and price depends on your location. Be warned these weigh over 200lbs you will need a battery space where you can lower them in with the boom and good straps! If fitted on top of the keel (ideal) use a waterproof vented box.
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Old 17-07-2020, 10:23   #21
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Re: Best batteries for $2k budget

8 AGM golf carts from NAPA (DEKA/East Penn) might be an option. I got mine for about $186 each when they were on sale. 220AH @ 6V. Slightly less life cycles than the Fireflys maybe. I almost went fireflys but not sure they actually operate as advertised. Time will tell.



X2 on an externally regulated 100A alternator and would add a temp sensor to that.
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Old 17-07-2020, 11:19   #22
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Re: Best batteries for $2k budget

Very happy with my Fireflys
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Old 17-07-2020, 12:05   #23
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Re: Best batteries for $2k budget

Thanks again for all the reply's.

Smac99, if i could afford 8 firefly's i would go LFP.

So it looks as though the decision is between 4 fireflys or 8 trojan t105's of which im leaning towards the larger and cheaper bank of t105's.

Thank you all for your advice.
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Old 17-07-2020, 12:47   #24
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Re: Best batteries for $2k budget

My vote and it’s been my vote for over 10 years LIFELINE AGM’s.
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Old 17-07-2020, 13:35   #25
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Re: Best batteries for $2k budget

Take a look at PASCO and their 6V AGM's. I just replaced my Lifeline's with their Precision and they seem to be doing great. JMHO
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Old 18-07-2020, 03:44   #26
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Re: Best batteries for $2k budget

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So it looks as though the decision is between 4 fireflys or 8 trojan t105's of which im leaning towards the larger and cheaper bank of t105's.

You might compare costs of 8 Lifeline 6V AGMs (T-105 equivalent). Sort of a (high) middle cost ground between FLAs and Fireflies. When I asked our local dealer if they'd match internet prices... the did.

OTOH, if you don't have issues with servicing FLAs, they're probably pretty good bang for the buck.

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Old 18-07-2020, 04:43   #27
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Best batteries for $2k budget

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Originally Posted by roland stockham View Post
At 250a\hr per day ... close to a 1000a/hr .... 80-100A/hrs per day ... 400A/hr fla bank...
... of your banks A/hr so you... give max 70a/hr ....

Oh dear, SIX misuse of unit notation penalty points applied to this post. :^)

But you were trying, so you get let off with a warning.

Correct notation shown here:


https://en.wikipedia.org/wiki/Ampere_hour
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Old 18-07-2020, 05:28   #28
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Re: Best batteries for $2k budget

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You might compare costs of 8 Lifeline 6V AGMs (T-105 equivalent). Sort of a (high) middle cost ground between FLAs and Fireflies.
They aren't!! The only practical difference between T105 FLA and any AGM is that you don't have to water the AGMs. For the most part all other "advantages" are marketing mumble jumble and they all have the same disadvantage of partial state of charge and capacity loss.

The VERY partial difference between FireFly and FLA/AGM is you can discharge them deeper and NOT fully recharge them right away and they will not suffer sulfation and capacity loss for it. The ability to remain in a partial state of charge and not suffer sulfation is a MAJOR advantage for an off the grid cruiser/boater. They are like LFP batteries without the worry of overcharge.
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Old 18-07-2020, 05:44   #29
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Re: Best batteries for $2k budget

Does anyone have experience with Narada Carbon batteries?
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Old 18-07-2020, 06:09   #30
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Re: Best batteries for $2k budget

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Does anyone have experience with Narada Carbon batteries?
I have never heard of them and looked it up. Seems to state similar to Firefly, but without much details.

You should state a new thread!
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