5 Years ago, I designed and built a 12V battery based on cells sold at battery hookup. It's been running every day since October 17 2021. The cells are 3.2V 600mAh. I have a battery balancer attached to the cells which very rarely illuminates. The arrangement is 9 in parallel, 4 Series so 4S9P. It works great in winter and summer, no issues at all. If you are planning on doing something like this, you can definitely do it on your Prius. I cannot say the same for other cars. I would not jumper other cars from a battery like this either. But anyway, screw lead acid batteries, they never last 2 years in Washington State weather. Here I have proven that LifePo4 can do 5 years without any issues. The battery looks like new on the outside and on the inside. It changes fine and the car has not stalled or left me anywhere stranded since. Original post a the other place before I was banned for whatever stupid reason. https://www.reddit.com/r/prius/comments/qacx7w/im_testing_my_32650_12v_lifepo4_battery_after/
Why wouldn’t you want to jump other cars? Wouldn’t the pull on the battery be similar or did you have a different concern?
Looks good btw. I still half want to do something similar for battery backup on the house. Not a priority at the moment though.
Not an expert but regular cars need way more current to start the full gas engine than the Prius C needs. Hundreds of "Cold Cranking Amps", whatever those are.
That is why this battery is fine in the Prius C but not for jump starting a regular combustion engine.
It's essentially how much current can the battery supply to start (crank) the engine at it's minimum service temperature - essentially the worst-case minimum current it can supply. Bigger engines need bigger starter motors to overcome inertia, which needs more power to work. Since the battery is fixed at ~12V, more power means more current.
Home battery backup was my first thought here. First I've thought about it. I wonder how much it would cost vs comparable commercial solution.
I wouldn't DIY now, There are plenty of LiFePO4 batteries on Amazon for like $130 bucks with double the specs on my DIY.
yes but i don't trust amazon for batteries.
My message is to just go with LifePO4. Its safe chemistry and it just lasts a lot longer than lead acid.
I built a DIY 280ah lifepo4 battery 4 years ago for about $450. Its nuts that in 2026 you can get probably double the capacity already assembled for probably less money.
Just make sure you do not buy one of the fire hazard batteries!
I'll have to take some pictures to send! LOL
well I soldered all the nickel strips to the batteries and in between. if you heat up those strips accidentally, you'll have a lot of fun sparks and the magic smoke will start leaving your vehicle. Its not 100% safe, maybe 80% to 90%. But you know, I am plenty happier to be carrying around a known minor safety hazard that might cause some smoke than carrying a pile of acid inside the cabin. Outside the passenger cabin, who cares. But inside, yeah that battery will smoke if it gets heated or impacted. And I know the hazard, I think its safe up to and beyond 15G's which is the standard for vehicle components. In contrast, I have no clue how other batteries are put together from other vendors, so my life is being weighed against someone's profit. The internals are probably separated using glues and tape. Mine has all internals separated with 1/8" FR4. The outside of my battery is 1/4" thick plastic. if mine goes up in smoke I'll probably smell stuff, stop the car and have plenty of time to go disconnect it. VS: hey your car is on fire. I have pace of mind and my confidence only grows each day that thing is in there.
Battery spot welders can be had for really cheep now. I just picked one up for $40 so I can make my own packs for solar projects. Just need to get me a lot of cells.
Yup, I got one at a later date for a different pack. Its generally a good idea to not heat the terminals on lifepo4s or other batteries with the safety cap.
Hi, idiot here, and maybe I'm wrong since I have zero clue how any of this works.
That being said, wouldn't you limit how hot it would get if you limited how much charge it allows itself to push?
Like if you put in some kind of capacitor, or voltage regulator. Sure, it may charge slower, but if you know it can handle 15Gs, and you regulate it for 14Gs, wouldn't that eliminate the heat? And charge slightly slower, but 100% safer?
It should be fine. I'm just not comfortable with solder joints where the joint could be disordered and just fall off. The sonic or spot welders are safer that way.