DIY Lifepo4 RV Battery

todd · August 2020

I have issues with flooded and SLI batteries and looking for something better, after building a ebike the lights came on and I decided to do a costs analysis on building replacement 4D and 8D sized batteries using LiFe cells. The retail market prices for these are obscene, $1,800 to $2,500 and up. I suspect I could do better. The 8D battery will used for engine starting and need to supply 300 to 400 ahr or the equivalent of 1600 cca, the 4D batteries can be about 200 ahr. I am thinking of 18650, 26650 or larger cells, Anyone care to comment on this project

Photowhit · August 2020

If think you will need a separate starting battery. I believe most auto starters are designed based on allowing as much energy to pass through the starter as possible, limited by the batteries ability to send current. Lithium has nearly an unlimited capacity to send current.

Lithium jump packs use to regularly melt the wires because people failed to remove them after the car started. I think the one I have now is timed only allowing for a 20-30 second connection.

Perhaps things have changed with auto manufactures dealing with lithium cars and hybrids. I think the Prius still has a lead acid starting battery, though that might be a version or 2 back... CCA won't be a problem, they have lithium jump packs that aren't much larger than a pack of cigarettes'.

softdown · August 2020

Makes absolute sense in your case:
Much smaller and lighter
You seem to gave Li-ion experience via your ebike.

I argue for LFP/LiFePo4 due to increased safety and longevity. Takes more space than Li-ion but much less than lead acid. 32650 seems the norm for LFP solar. Prismatic are multitudes easier to assemble. I think 18650s are pretty much in the NMC arena - higher performance but shorter life. Plus the risks of nickel and cobalt. Though alternatives are out there. Good book on DIY Lithium: https://www.amazon.com/gp/product/0989906701/ref=ppx_yo_dt_b_asin_title_o03_s01?ie=UTF8&psc=1
I reviewed it last night in fact. Spot welding is the way to go. Soldering the tops of lithium batteries damages them - maybe 10%.

Lead still has merits for home solar. Not so much in an RV. But do not charge lithium that is 32F or colder. It kills it.

mike95490 · August 2020

Just remember - can't charge any Li battery below frost temps. Under a car hood can get far below that in the winter, and car charging systems don't have any thermal control for this.

softdown · August 2020

Thought he was seeking energy storage. Even Tesla reportedly uses lead acid for starting systems.

todd · August 2020

I failed to mention I'm trying start a Cummins L10-300 diesel, yes the L10 is 10 litre. The 1600 cca is about the min desired bat size. I tried using a 1200 cca and that bat lasted just about 3 years. At over $250, there has to be a better alternative. The $10,000 question is can you get enough Amperage from LiFePO4 batteries to do what is needed. A few years ago I replaced a phone battery and accidentally shorted it. The battery got very hot and I barely had enough time to get it removed from the phone and outside before it caught fire. That will be the last time I use Li-ion as a power source if give a choice. The ebike is using 4 12 v lifepo4 batteries, a big bigger but they do catch fire if damaged. So I have to build a temp controlled battery warmer too.. uggh...

BB. · August 2020

There are companies/trucking firms that are using "super capacitors" for starting current with big diesel engines--Especially in sub freezing climates where Li Ion batteries are not a good fit (as I understand from a quick reading of some links):

https://www.polarpower.com/wp-content/uploads/Supercapacitor_0115.pdf
https://www.maxwell.com/products/esm/

No experience with them... Just an option to look at.

-Bill

softdown · August 2020

I have a 2017 Duracell 8D by East Penn. Still putting out almost 1500 CCA with internal resistance a bit over 2. Some Sam's Club stores carries them for $200. I just can't see a DIY LiFePO4 battery for a starter battery - unless you have a connection and experience for the cells.

todd · August 2020

I have a 2016 8D purchased from car quest that was used less than a dozen times, iirc I paid apx $300 for it. I had it on a 2 amp trickle charger, when I went to check on it this spring I found the electrolyte had dropped below plate levels, I refilled and charged but not enough cca capacity to turn over the engine. very frustrated with lead batteries. The 10 yr life span of lifepo4 batteries got my attention, the 30 yr lifespan of lto even more so.

BB. · August 2020

I suggest that you check the trickle charger you where using... I have found the "cheap" trickle chargers would not hold "float voltage" (around 13.2 to 13.6 volts), but would simply continuously dump current into the battery, raising the voltage >>14.0 volts -- And "boil" (actually "gas") the battery and cause it to lose water--Exposing the plates in a few months.

I have used a couple of much better float chargers (ranging from ~$40 to ~$140+), and checked that they either floated at ~13.5 volts, or would charge to 14.x volts, then shutdown until the battery drifted down to 12.7 (guessing) or so, then charge again to 14.x volts... These chargers never "used water" in the batteries.

https://www.amazon.com/BatteryMinder-128CEC1-Charger-Maintainer-Desulfator-Motorcycles-Snowmobiles/dp/B01D3SWXUA (BatteryMinder, programmable, expensive)
https://www.amazon.com/BatteryMINDer-Model-2012-Maintainer-Motorcycles/dp/B005EKY1EM (BatteryMinder, not programmable, cheaper)
https://www.amazon.com/Duracell-DRMC4A-Lithium-Battery-Maintainer/dp/B07MW39STH (Duracell, works well, supports Lithium Ion, less expensive)

I have used all of the above... The first two for many years on cars that were not driven often (and had Lojack, cell phone, computers, etc. that would take the battery dead in one to several months at times).

Battery Tender also makes some good float chargers (as I understand). Sometimes Costco has the Duracell and BatteryTender (Battery Tender model currently on Costco.com).

Check the battery voltage when float charging--And see if they are above the "Gassing Voltage" (~14.34 volts @ 25C, drops as battery temperature rises).

https://www.powerstream.com/SLA.htm

I did use a "cheap and dirty" method with non-float chargers... Use a cheap 120 VAC timer set to run the charger 1 hour per day. It worked OK, but my system "failed" if the vehicle owner left something on (forgot to close trunk, leave a door cracked open, the 12 volt light would drain the battery and 1 hour per day was not enough to keep up). Ended up with using a "real float charger" and those problems (intermittent loads discharging battery) went away.

I would not suggest these float chargers for "cycling" batteries--But for batteries sitting unused/floating--Never had any problem.

And as an FYI... The above charges (seem to) have current regulated outputs. I used a cheap 1 amp 12 volt "cube" charger on a dead battery to start the car and move it... The dead battery drew so much charging current that the transformer in the cube charger overheated and popped open the case (no fire or smoke, and charger did continue to work). The cheap chargers for floating batteries--Not worth the money (in my humble opinion).

-Bill

softdown · August 2020

in a somewhat cold environ I have seen a lot of lead acids be usable for 9 years. It is the care of the battery - not what it is made of. Many lithium batteries have been quickly destroyed by overcharging and over discharging and charging while freezing and charging with too great of current. It is quite often the BMS that goes first - but at least 95% will give up when the BMS goes.

I'd say lithium is a bit more delicate than lead acid. LTO is something that exists - somewhere. Still very expensive. I know a guy who persevered and got some. They under produced published ratings by 30% - he decided they must have been used. All of us get excited when we see the lifespan on LTO. But I have yet to see them for sale in the US. I'm sure Ali Express has offerings but most people get a "surprise" when their package eventually shows up.

Maybe a truckers board will have a few who have tried it. We don't even have a trucker here - and all but a few still use lead for solar power. I am close to buying some LiFePO4s though - for prepping purposes. My lead batteries should last another 3-4 years. But LiFePO4s are uniquely situated to storing that long with little damage. I can't realistically buy lead for usage in 4 years - the batteries would be half expired by 2024.

todd · August 2020

how about running 20 or so small batteries in parallel ? using my ebike batteries for example, and
looking at the specs, I see a max continuous discharge of 42 amps , max peak of 80 amp, doing the math 840 amps continuous, 1600 peak, total cost is $900 plus tax. I'll need to see if 20 + batteries will fit the battery box. btw these are the same battery I've used on my ebike 4x in series

softdown · August 2020

Would need a robust BMS to handle life on the road - not to mention massive cables for the current draw. Add $300 plus installation, Unless magic smoke intrigues you.

DIY Lifepo4 RV Battery

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