Another house battery option?

gatorgrizz27

Active member
I stumbled across these after reading an electric vehicle thread on here, and they seem like they might have some real benefits unless I’m missing something.

Lithium batteries have become popular, but they are around $1,000 for 100ah and still have the standard battery form factor.


These are 3.2v each, 72ah, 4 lbs, and $139. Four of them in series would give you 12.8v, 72ah, 16 lbs, and $556.

The real benefit is that they are 8.5” x 5.5” x 1.18”, so they could be stashed away behind the rear plastic trim panel, under or behind seats, in a cubby, etc.

Am I missing something that would keep these from being a great option for our vehicles?
 

john61ct

Adventurer
No, these are the standard and best way to use LFP as a House bank, been discussed over many years.

Besides CALB, Winston, GBS, and Sinopoly are great cells.

Cared for properly can last decades, twice the energy density, very little voltage sag, great for 12V or 24V systems.

Would not consider using the "drop-in" style myself.

But either way, by the time you're done, LFP costs at least 7x the investment up front, so if you mess up and murder them in less than 25 years, there goes your ROI.

From that POV, 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. NAPA relabels it here: https://www.napaonline.com/en/p/NBP8144 Deka self-labeled also sold at Lowes.
 

gatorgrizz27

Active member
Yeah, I’m running a pair of Insterstate golf cart batteries in my trailer. For value and handling abuse they are the way to go for sure. Not ideal for inside a vehicle though due to space/weight.

With the ability of lithium ion to be discharged so far past what lead acid can stand, 72 ah should be sufficient for most uses. If you’re looking at ~ $200 for an Odyssey/Optima, $550 isn’t a huge stretch.
 

shade

Well-known member
Yeah, I’m running a pair of Insterstate golf cart batteries in my trailer. For value and handling abuse they are the way to go for sure. Not ideal for inside a vehicle though due to space/weight.

With the ability of lithium ion to be discharged so far past what lead acid can stand, 72 ah should be sufficient for most uses. If you’re looking at ~ $200 for an Odyssey/Optima, $550 isn’t a huge stretch.
You'd also have to factor in the supporting management system, and some type of housing.

Still, DIY LFP banks are objectively cheaper, and can be better than off-the-shelf solutions, especially "drop-in" batteries with whatever uncommunicative management was installed by the manufacturer.
 

jonyjoe101

Adventurer
72ah lifepo4 is comparable to 144 ah lead acid. 16 pounds versus over 120 pounds plus. 500 dollars ain't bad for 72ah of lifepo4. They are easier to maintain then lead acid, unlike lead acid you don't have to fully charge everyday, you can leave them at 50 percent for months at a time with no damage, you can take them down to zero percent with no damage, they will still last you years. At slow discharge rates you get the full 72ah at high discharge rates you might get 68 ah, the difference won't be that large like lead acid.

Using a good bms like the chargery bms8, which I use (cost about 100 dollars) and you can charge with any method solar/alternator/AC, you need a good bms that is reliable. Also with lifepo4 you need a coulombmeter (tk15 or comparable) to count the amps, you can't track lifepo4 SOC with voltage since lifepo4 resting voltage is usually about 13.3 volts all the time.

The only drawback is you have to put the cells together yourself, but they sell all the parts for that. It's only 4 cells so it don't get any easier then that. My 220ah lifepo4 I built has 160 cells and I had to tab weld them all, the calb cells you just bolt them together. The only safety hazard with lifepo4 is don't puncture them, that will start a fire everytime, if you puncture a lead acid it will just leak acid everywhere. Just like lead acid, use fuses everywhere they can discharge alot of amps quickly.
 

shade

Well-known member
Taking LFP down to 0% SOC will shorten cell life. Same goes for most (all?) battery chemistries.

As temperatures approach 0*C, LFP won't accept a charge, and can be damaged if charging is attempted.

LFP cells are far less prone to burning than other lithium chemistries.

LFP can damage an alternator if the charge rate is too high for too long, creating too much heat.
 

rayra

Expedition Leader
First look seems appealing. And I could easily fit (4) of them in the space of my under-hood Aux Grp78. 280Ah for $600. (5) Grp78s would cost just as much and take 5-6x the volume and 10x the weight.
Their thinness also means you could make a floor deck sandwich out of the things that would only cost you a couple inches of cargo deck height. For a true off-grid long-duration sort of need they look like they'd be well worth the money.
 

gatorgrizz27

Active member
First look seems appealing. And I could easily fit (4) of them in the space of my under-hood Aux Grp78. 280Ah for $600. (5) Grp78s would cost just as much and take 5-6x the volume and 10x the weight.
Their thinness also means you could make a floor deck sandwich out of the things that would only cost you a couple inches of cargo deck height. For a true off-grid long-duration sort of need they look like they'd be well worth the money.
Yeah the size of them plus the cost compared to stuff like the Battleborn is what caught my attention. Unfortunately the amp hours don’t multiply when you’re running them in series. They are 3.2v, 72ah, so 4 in series would be 12.8v, still 72ah. However more of that capacity is usable than a lead acid battery, which tapers off and shouldn’t be run below 50% for longevity.

Running batteries in parallel will increase the amp hours, so if you bought 8 cells you could wire 4 in series then each bank in parallel, giving you 144ah.

I was thinking you could pull one of the plastic rear panels off and stash at least 4 of them around the wheel well area.
 

rayra

Expedition Leader
yeah I brainfarted on that, had originally posted I could fit (6) in the same volume as my Aux, but then thought about the serial connection and changed it to (4) and forgot all about the Ah.
Yes, they could be tucked away in a lot of othewise lost volume behind trim panels. I'm still liking the floor sandwich idea too. Wouldn't really miss a couple inches of storage height. Would be like a Tesla Power Wall, but on the floor. Could fit a nice array in an given cargo deck area. serial and parallel, with a phat 12v connector set in the rear edge. Or an array of 12VDC ports / inverters, all in a row.
Or a slim upright array, just taking 2" to the side of a cargo area, same rear edge arrangement of ports / connection options. Shore power, solar power, charge it up before your trip, a real slim power pack. 3" thick, 10" tall, 2' long

As sechsy as those packs are, they're still comparatively very expensive.

Three years ago while planning my own cargo area power module I was (still am, sorta) considering using some compact 12V SLA like the kind used in wheelchairs and mobility carts. They were $75 for (4) 10Ah and not very big. I figured an arrangement in otherwise empty volume. They'd get charged by the vehicle or solar, but be wired with a fat diode so they'd only provide power to the rear ports in the module. It would be an inexpensive method to boost my stored power by ~25%. I might still do it.

Got so far as making some wood block mockups for trying out different arrangements, before I got distracted working on other projects.

 
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luthj

Engineer In Residence
There are lots of folks making 4S DIY packs with prismatic cells. Though the USA supply is starting to dry up, as Chinese factories have been idle for a while now. The Chinese MFGs have really been pushing the LFP battery tech. Its gotten to the point where energy density is that far off from lithium cobal chemistry.
 
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