Let’s see how quickly I regret making this post.

[Cthoops]

We have been living and cruising on our 30’ sailboat since August, 2018. About six months before we left, we installed two Firefly batteries and have ignored them ever since. Time marches on, however, and it looks like we may need to install new batteries soonish.

Unfortunately for us, Firefly batteries shot themselves in the foot with quality control issues and are no longer an option. We are 100% set it and forget it people when it comes to batteries. The subject of electricity is not our strong suit. We’ve lightly researched going with Lithium but they strike us as a bit more complex than we prefer. Plus, we may buy a larger (38 foot maximum) boat in the future so we aren’t sure we want to go down the road of the all-in expenses of lithiums.

We have minimal needs when it comes to electricity. Our boat is 100% 12-volt, we don’t have shore power capability, and although I don’t have our 24 hour usage in front of me, I’m pretty sure I recall that we use a maximum of 30 ah every 24 hours when we aren’t on a passage. It jumps up on a 24+ hour passage because of the instruments.

Having said that, if we bought 2, 100A AGM batteries, and they are kept charged by 2, 100W solar panels plus a 70 amp alternator when we are motoring, how long could we expect them to last? I know they won’t handle a partial state of charge as well as our Firefly batteries do, but they won’t be drawn down much at all. We typically cruise up and down the US East Coast and winter in the Bahamas. Or should we suck it up and deal with the learning curve and higher maintenance of lithiums? Thanks.

[Mike OReilly]

Holy Schmoly Batman, with such a small demand you could probably get by with a bunch of AA rechargeable.

OK, I jest. But that is a very small electricity demand. I suspect you 200 watts of solar will easily keep up with the charging of your new AGMs. Certainly the 70 amp alternator is way more than needed. It should charge those babies in no time.

[Chotu]

The thing is, you would only need one 100AH lithium battery in this case.

That’s a pretty low expense if you get a drop in.

Less than $200 for the same brand I've been using every day for years now

I know there might be a little bit of an expense with the alternator, however

certainly, they would handle the partial state of charge a lot better

[newhaul]

Originally Posted by Cthoops

We have been living and cruising on our 30’ sailboat since August, 2018. About six months before we left, we installed two Firefly batteries and have ignored them ever since. Time marches on, however, and it looks like we may need to install new batteries soonish.

Unfortunately for us, Firefly batteries shot themselves in the foot with quality control issues and are no longer an option. We are 100% set it and forget it people when it comes to batteries. The subject of electricity is not our strong suit. We’ve lightly researched going with Lithium but they strike us as a bit more complex than we prefer. Plus, we may buy a larger (38 foot maximum) boat in the future so we aren’t sure we want to go down the road of the all-in expenses of lithiums.

We have minimal needs when it comes to electricity. Our boat is 100% 12-volt, we don’t have shore power capability, and although I don’t have our 24 hour usage in front of me, I’m pretty sure I recall that we use a maximum of 30 ah every 24 hours when we aren’t on a passage. It jumps up on a 24+ hour passage because of the instruments.

Having said that, if we bought 2, 100A AGM batteries, and they are kept charged by 2, 100W solar panels plus a 70 amp alternator when we are motoring, how long could we expect them to last? I know they won’t handle a partial state of charge as well as our Firefly batteries do, but they won’t be drawn down much at all. We typically cruise up and down the US East Coast and winter in the Bahamas. Or should we suck it up and deal with the learning curve and higher maintenance of lithiums? Thanks.

Ok here's the simple of it first do you like bluetooth?
Secondly what charge controller does your solar run through?
Lastly do you like saving money?
With your apparent power needs a single 100ah lifepo4 drop in battery a 40 amp dc2dc charger and reset your solar controller to stop charging at 13.8v gives an 85% charge and will maximize the cycle life of the battery.

https://www.amazon.com/Battery-Charg...hvexpln=73&th=

This battery has lots of Bluetooth available data

https://www.amazon.com/gp/product/B0...12121955H&th=1

So for just over $300 USD you just upgraded to lifepo4 .

[boatpoker]

A pair of 6v golf cart batteries in series parallel will do what you need and no wheels need be reinvented. Ours last about 8 years of full time living/cruising aboard and can be bought on sale for under $100ea ... no BMS, questionable Chinese "drop in" lithium, isolation switches (from your start battery) or DC to DC chargers required.

[newhaul]

Originally Posted by boatpoker

A pair of 6v golf cart batteries in series parallel will do what you need and no wheels need be reinvented. Ours last about 8 years of full time living/cruising aboard and can be bought on sale for under $100ea ... no BMS, questionable Chinese "drop in" lithium, isolation switches (from your start battery) or DC to DC chargers required.

And about the same price as the new lifepo4 batteries which are 1/3rd the weight and 10 times the life as lead not to mention no PSOC issues and no maintenance issues of gc2 lead batteries

[senormechanico]

I agree with Newhaul.


Between my boat, (lithiums), home (solar grid tie and lithium backups) and car, (Tesla Model S) I have only one lead acid.


It's a 30 aH in the Tesla for running pumps, power steering etc, and which is charged by the lithiums.

When the time comes to replace that lead acid battery, it's getting a lithium in its place.

[Chotu]

Originally Posted by senormechanico

I agree with Newhaul.


Between my boat, (lithiums), home (solar grid tie and lithium backups) and car, (Tesla Model S) I have only one lead acid.


It's a 30 aH in the Tesla for running pumps, power steering etc, and which is charged by the lithiums.

When the time comes to replace that lead acid battery, it's getting a lithium in its place.

I know what you mean. I have a couple of lead acid starting batteries. I can’t wait to get some drop in starting batteries going.

I have a lithium starting battery on my motorcycle and it has saved my bacon so many times. Somehow I don’t take care of motorcycles like I do boats. I kept putting it away and forgetting to unhook the battery so the battery was dead every spring.

I figured after a couple times of this I killed the battery like you would with Lead.

instead? The BMS took care of everything and cut the battery off before any damage could occur.

all I had to do was put a pair of jumper cables on it, and it was good for the rest of the year.


then recently, I really messed up. I was upgrading from my construction level wiring on the boat to permanent wiring. I dropped the positive battery cable onto a negative terminal. Direct short with double ought cable. No fuse. I was ready for an explosion ha ha.

there was a tiny little spark, and then nothing. The battery had no voltage. 20 minutes later, the battery was back on. the BMS took care of that big mistake.


the ease of use is like a whole different world

[thomm225]

I finally went with 6 Volt Golf Cart Batteries after about 10 years using various types of 12 Volt Batteries.

Usually, I had two in parallel, but they still were not as strong as the two Golf Cart Batteries in Series.

The Gold Cart Batteries are much bigger than the 12's.

They are much better than 12 Volt Batteries, and they never get low like my 12s did overnight with fans etc. running all night.

I installed two 6 Volt 220 AH Golf Cart Batteries around about 2020, and they have been great.

I paid around $335 for the pair.

I have no shore power or alternator. Just solar and my gold cart batteries.

[ranger58sb]

Originally Posted by Cthoops

We have been living and cruising on our 30’ sailboat since August, 2018. About six months before we left, we installed two Firefly batteries and have ignored them ever since. Time marches on, however, and it looks like we may need to install new batteries soonish.

Unfortunately for us, Firefly batteries shot themselves in the foot with quality control issues and are no longer an option.

We have minimal needs when it comes to electricity. Our boat is 100% 12-volt, we don’t have shore power capability, and .... I’m pretty sure I recall that we use a maximum of 30 ah every 24 hours when we aren’t on a passage.

Having said that, if we bought 2, 100A AGM batteries, and they are kept charged by 2, 100W solar panels plus a 70 amp alternator when we are motoring, how long could we expect them to last? I know they won’t handle a partial state of charge as well as our Firefly batteries do, but they won’t be drawn down much at all.

Your Firefly batteries have lasted 6 years? Have you tested first to see if you actually need to change anything yet?

I'd guess you'd get the same from either Odyssey or Lifeline AGMs... maybe also same from almost any other brand of AGMs. (Lifeline has some 6V models.)

We've gotten as much a 11-12 seasons from Odyssey banks, although that's been with shorepower and occasional genset charging. Sounds like your solar is good enough to avoid extended PSOC.

And they're just batteries. Consummables.

-Chris

[Sparx]

Originally Posted by Cthoops

Having said that, if we bought 2, 100A AGM batteries, and they are kept charged by 2, 100W solar panels plus a 70 amp alternator when we are motoring, how long could we expect them to last? I know they won’t handle a partial state of charge as well as our Firefly batteries do, but they won’t be drawn down much at all. We typically cruise up and down the US East Coast and winter in the Bahamas. Or should we suck it up and deal with the learning curve and higher maintenance of lithiums? Thanks.

I have 200 Ah of AGM on my boat supported by 600W of solar. This set up is 6 years old and operates very reliably. However it has becomes abundantly clear that the slow charging rate of the AGM limits the output of the solar. I expect Lithium would not have this problem and would be able to harvest much more power than the AGM.

When the AGM gives up they will be replaced with Lithium.

[newhaul]

Originally Posted by thomm225

I finally went with 6 Volt Golf Cart Batteries after about 10 years using various types of 12 Volt Batteries.

Usually, I had two in parallel, but they still were not as strong as the two Golf Cart Batteries in Series.

The Gold Cart Batteries are much bigger than the 12's.

They are much better than 12 Volt Batteries, and they never get low like my 12s did overnight with fans etc. running all night.

I installed two 6 Volt 220 AH Golf Cart Batteries around about 2020, and they have been great.

I paid around $335 for the pair.

I have no shore power or alternator. Just solar and my gold cart batteries.

When they die and that will likely happen in about 2 or 3 years.
Switch to a single 100ah lifepo4 . Cost is less than one of the 6v you have now and the voltage does not sag like fla do you will see around 13v for the entire 80ah usable out of the battery. Also you will love the charge curve faster charge
The biggest difference is the weight. You will happily lose about 3/4 of the weight and 100% of the maintenance.
If you don't need Bluetooth on the battery you can get one with American warranty coverage for about 150 now or 200 with Bluetooth connectivity.

[s/v Jedi]

For a decent decision on what to do, you need to answer these questions:

- where in the world are you?
- what brand/model solar controllers do you have?
- what brand/model alternator and regulator do you have?
- you don’t have any other charger?
- do you have an inverter? Brand/model?
- space dimensions where batteries are installed?

[Cthoops]

We’re not entirely certain we need to replace them just yet. The cabin lights have been intermittently dim, but the Engel fridge is running fine. We’ve had a string of cloudy days, but that hasn’t been an issue for us in the past. We just checked them with the multimeter and they were reading 11.6 volts and 11.5 volts, but now it’s sunny so we’ll see how they bounce back. And they will actually be seven years old in February.

Regardless, they are reaching the end of their useful life span, and we’ll want to replace them one way or another before we head to the Bahamas in another year. If we don’t, they will undoubtedly fail while we are in the Bahamas and whatever we can get to replace them with will cost 2-3 times as much. So we are debating replacing with lithiums vs. AGM. Saving weight with lithiums is VERY appealing, but simply dropping in two AGM’s is also tempting.

If we switch to lithium we would need to replace the two controllers for our solar panels, but we do have an external regulator for our alternator that we haven’t installed yet. As a side note, we don’t use a separate starting battery.

What else would we need to buy besides the controllers if we switched to lithium? We don’t use an inverter on the boat. We have LED lights for everything, an Engel fridge, the standard cockpit instruments, an AIS, an SSB, an electric windlass, four fans, a small fan for our composting head, and no pressure water. Overall, it’s a pretty basic boat.

[donradcliffe]

Tell us what solar controllers and panels you are using, and we can tell you whether they need replacing. The drop in lithium batteries are cheaper and lighter than AGMs, and should last many times as long and be easier to charge. Another issue is the current you need to start your engine. You may be better off with two drop in 100 amp lithiums than one two hundred amp lithiums.