Recommendations for Group 31 AGM replacement with LiFPO4

[svspirited]

Our current AGM battery bank is coming to the end of its useful life, they are about 6 years old now and starting to lose charge pretty rapidly, the solar is keeping things alive when it is sunny out but when the clouds roll in the bank dies off pretty quickly. The current setup is 6x96ah group 31 AGMs with a Magnum inverter/charger that works really well. I have been looking at the GreenLife brand which claims to be a drop in replacement for the battery we currently have with a simple reprogram of the charger to charge at the correct levels for Lithium. They do have an onboard BMS so I think I can buy the six batteries and drop them in to the existing boxes and in theory be good to go with a good bit more useable power and a little less weight.

Does anyone have experience with this brand? Any others you would recommend? Is the idea of a simple drop in replacement reality or marketing hype? I've done some searches on the forum and the opinions appear pretty mixed on that topic but only a few were real world examples where it appears to have worked out just fine.

[Inkog]

I have a couple of BattleBorn "Drop-ins" in my RV and love them. Although I designed my system around them. While its true that you can charge them with a typical Lead-acid AGM charger, you'll get a longer life out of them if you can configure the charge profiles to their ideal needs. I think the higher cost of drop-ins is what turns most people off, but it is certainly the easiest way to make the switch to LiFePo.

[john61ct]

Putting more than 2-3 series strings (as each 12V unit is, 4S) in parallel can lead to shortened lifetimes from balancing issues.

I am very skeptical that drop-ins have the same quality of manufacturing, purity of chemicals etc.

Who is the actual manufacturer of the cells internally?

It is a very dicey market, thousands of small Chinese companies competing in sometimes shady ways, very little transparency no decent word of mouth.

I think very unlikely they will have the lifespan of Winston/Thundersky/Voltronix, CALB, GBS, Sinopoly. And so little collective experience has accumulated wrt drop-ins, this factor won't be know for decades

They may even mask the fact that the batt is LiPo or NMC rather than LFP, very very short-lived.

Drop-in 12V interior BMS is opaque, can't be adjusted or disabled, no communications to the outside, and they can suddenly isolate the battery with no warning.

Special steps must be taken to ensure this can't damage charge sources or sensitive load devices.

Terminating charging when full, or when temps get too low or too high, should be able to signal other*gear, or controlling generic relays.

As opposed to simply taking a batt offline without warning, which load dump can cause damaging spikes/surges.

The BMS can't be bypassed, even to check on the cells' voltages, and often drastically limits charge / discharge C-rates to a tiny fraction of LFP's capabilities.

LFP is usually capable of accepting very high charge rates, no problem. To the point that 2-3 day's worth of energy can be pumped back into the bank in an hour or two if you have a high-current charge source available. But the cheap included BMS in drop-ins prevents that, restricts you to a slow charge (and discharge) rate.

Check to see if they even allow serial or parallel connection into a bigger bank?

Allowing the "Full" or "Too Low" setpoints to be adjusted by the user to extend lifespan. The balancing function may require a charge voltage that is higher than what you want for longevity.

Allowing the user to even **see** the state of cell balance, verify that BMS function is working.

Allowing a cell to be swapped out if one proves faulty.

All impossible with drop-ins.

You have to understand, the whole "drop-in concept" is a lie if you want longevity, you need a ​good system, all the infrastructure designed for LFP from the ground up*

not just BMS
over-current protection
LVD and HVD safety cut-offs
temperature protection

but also
100% PROGRAMMABLE charge sources
IMO a separate charge and loads bus

Finally for a large bank, they're rarely cheaper, might as well get a packaged system from OPE-Li3 (Lithionics/Ocean Planet), Victron or MasterVolt.

Super B looks worth checking out also.

[smac999]

look at the firefly agms. They are drop in group 31.

No lithium is drop in. They are very complicated and advanced to do correctly. And need a lot more r&d and use. I would have a back up agm bank in place for when it failed.

[john61ct]

Odyssey PC-2150 are likely better value than FF, unless you have unavoidable PSOC issues.

[john61ct]

But if the GC shape can fit your space, the best battery value by far is Duracell (actually Deka/East Penn) FLA deep cycle golf cart batteries, 2x6V, around $200 per 200+AH @12V pair from BatteriesPlus or Sam's Club. Deka labeled same batts also sold at Lowes.

[svspirited]

Thanks for the responses, I was hoping drop-in was a viable thing but clearly there are some factors there I'm not familiar with and maybe sticking with the AGMs will make more sense since much of the existing infrastructure, controllers, charger, etc is new enough to be a waste to swap it out.

[svspirited]

These look pretty interesting. Carbon Foam seems to have some pretty nice characteristics in terms of number of cycles, discharge rates, and charge rates and about half the cost of Lithium. Thanks for pointing those out, I hadn't heard of that technology before.

Originally Posted by smac999

look at the firefly agms. They are drop in group 31.

No lithium is drop in. They are very complicated and advanced to do correctly. And need a lot more r&d and use. I would have a back up agm bank in place for when it failed.

[john61ct]

http://www.cruisersforum.com/forums/...d.php?t=195243
http://www.trawlerforum.com/forums/s...d.php?p=604465

http://www.cruisersforum.com/forums/...es-173008.html

[admiralslater]

Originally Posted by svspirited

These look pretty interesting. Carbon Foam seems to have some pretty nice characteristics in terms of number of cycles, discharge rates, and charge rates and about half the cost of Lithium. Thanks for pointing those out, I hadn't heard of that technology before.

I am buying my second set of carbon foam Firefly batteries (dont ask)
When I asked a number of people who I trust about drop in lithium batteries.
None of them were enthusiastic, especially when put up against FF batteries.
The big reason other than reliability was the fact that the drop in battery that i was looking at would not accept amps as quickly as the Fireflys . I was told that this was because the internal BMS had to reduce acceptance for safety/reliability issues . This was a big deal for us as my loads and and charging capacity where all based on getting the FFs as fully charged as possible every day .
I had really hoped that the drop ins would work for me but they dont .
So if weight saving is your only priority then the drop ins might work .

[svspirited]

Interesting, weight's not an issue for us, full displacement mono-hull, a little weight savings would be nice but not really a driver. More the quick charge and ability to discharge more deeply. We've got a lot of solar and a generator to charge up when the weather turns grey for a few days.

[admiralslater]

Originally Posted by svspirited

Interesting, weight's not an issue for us, full displacement mono-hull, a little weight savings would be nice but not really a driver. More the quick charge and ability to discharge more deeply. We've got a lot of solar and a generator to charge up when the weather turns grey for a few days.

That is why we choose the batteries twice. You will need programable solar controllers ( i use victron) programable Battery charger ( I use sterling ) and external regulator on the alternator ( I use balmar) .
The Fireflys charge at 14.4 with float at 13.2.
Bruce Schwab is very helpful. Ocean Planet energy

[Inkog]

I just checked the prices and specs of a Firefly, and their is no way I'd go for them over a LiFePo. You still shouldn't go over 50% DoD and they are more expensive per usable Ah than LiFePo. According to the specs they can accept a 1C charge rate, but at their internal resistance <~5mO I wonder if that's possible at 50% DOD? Their 5hr capacity rate (standard) is 90Ah. I'd like to know what type of charge they'll take at 50% DOD. I bet it isn't anywhere close to 90A, I doubt if it even reaches .5C or 45A, its going to be the same as most VRLA AGMs.

They are twice as heavy and you can't add additional new batteries down the road as capacity diminishes, just like AGMs, you have to replace the entire bank.

[ranger58sb]

Originally Posted by svspirited

Our current AGM battery bank is coming to the end of its useful life, they are about 6 years old now and starting to lose charge pretty rapidly,

What AGM batteries do you have that lasted 6 years? Under what circumstances? Typical depths of discharge? How soon re-charged (presumably often, to the extent your solar system can do it)? Periodically equalized (if recommended)? How expensive?

I'm wondering if it might be whatever you had is good enough bang for the buck...

-Chris

[john61ct]

Originally Posted by Inkog

I just checked the prices and specs of a Firefly, and their is no way I'd go for them over a LiFePo. You still shouldn't go over 50% DoD and they are more expensive per usable Ah than LiFePo.

Please link to quality LFP cells cheaper than FF that do not require importing yourself from China.

And FF are just fine, uniquely so among AGM, going to 80% DoD.

Of course LFP will accept **much** higher C-rates, but regularly going over 0.3C hurts longevity, not a great idea.

Plus of course the design/BMS must allow it, which most drop-ins don't.

AGM thrives at the highest rates the will accept, better for longevity than slow charging.

Only use 20-hour rate for comparing lead chemistries, this stuff is confusing enough mixing in other rates.

I love LFP, not trying to push FF at all, each choice has different advantages for different use cases.