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/
I thought this was a bunch of cans of monster at first glance lmao
Same
This is not dull lol, this is awesome
thanks
yeah, and learning how to do this (which i want to) can teach me how to make ebike batteries.
there’s this kit where you just pay them like 75 bucks iirc and then you pop in a bunch of your old 18650s. i just don’t have enough old 18650s…
Although it’s tempting to have a battery pack where each cell can still be removed without welding/soldering, I would caution that this makes a poorer connection to the cell. For an e bike application especially, poor cell connection creates resistive losses at high currents, and the quality of the connection will be affected by road vibrations.
Whereas spot-welding is a firm attachment that won’t vibrate loose, nor is it as brittle as solder (which can break off if fatigued due to repeated mechanical stress). But if your use-case was stationary, then maybe this isn’t as big of an issue.
thank you for the information: i was, if i was going to do the kit we’re thinking of, going to either take a welding class at the community college and learn how to spot weld (my soldering sucks) or put damn good springs on each side of the batteries to maintain the connection. also orient the battery properly so bumps don’t jostle stuff loose.
I too took a welding class at my nearby community college, and it’s an awesome skill to have. That said, my understanding is that spot-welding for battery cells is substantially easily than TIG, MIG, stick, or any of the other large-format welding processes. Yes, PPE is still highly advised, but spot welding seems like something which can be picked up through watching a video.
Not to simplify too much, but a spot welder has only a few controls: the location of the weld, the current in amps, and the weld time in fractions of seconds. Some hobbyist tools specifically for battery packs will automatically execute a weld for the precise amps and seconds, provided that you make contact with the electrodes. Others have a foot pedal to start the weld.
Thank you for the encouragement, but I am a scardey cat and would feel better getting better training than YouTube
While I fully agree, it probably depends heavily on so you ask.
I would not jumper other cars from a battery like this either.
You can hook the batteries of the two cars up and just let the other car charge for like five minutes, this way there’s no current surge and presumably nothing should melt.
Learned this when I ran out of battery in the great outdoors and one car that’s rolled around was a Google Maps camera car. The driver said there’s so much electronics hooked up on his car that letting me start mine off his battery would shut his whole thing down.
Yea you also should have the car your are charging from run while charging yours and while starting so the alternator can help out with the current that is needed and the other batterie does not deplete to much.
Hell if you have a diesel with no batterie and a gas car with an empty batterie you could still start both by first starting the diesel with a roll start and then charging your batterie from their alternator while its running.
Who knew you could power a car with monster energy drinks
LOL! Monster in a box.
Lifep04 works great for things like this because they’re very good at taking on a full charge without damage, compared to lead acid. The Prius in particular doesn’t even need much of a 12v battery because it doesn’t provide the power to start the engine. It just does the lights, ECU, and it flips a 12v relay to start the car engine, which the bigger hybrid battery cranks over.
Also, to my knowledge, all Prius since Gen 2 (like 2004-2009) don’t come with a lead acid 12v battery and replacing one with a lead battery could cause you some warranty issues. If course, I’d imagine a home built battery could also cause a warranty issue. Lol
Really? I mean my Prius C is 2014. Its not lead acid. They use sealed lead acid batteries, which carry the current thru a gel. They are terrible in my experience. Any bubbling in the gel causes amperage loss.
You’re right I was thinking for some reason AGM batteries weren’t lead acid batteries, but they are.
oh you’re well outside warranty already. go nuts.
The final specs are basically: 12.8V, 691.2Wh, 54Ah. Its more than the Prius battery had previously except for the low amperage rating. The requirement for the Prius C is basically to click the main contacts on and to drive the air pump. Not much else runs from the 12V battery. Once the main battery is engaged all of the accessories are ran from the main battery. In the case that the main battery dies and you have the AC on and all the accessories running, this battery should be able to keep you power steering running for an hour, enough to safely stop the car and put it on park. Amazon has bigger beefier batteries. I’ve run this one for many days with the check hybrid system alert light on. Apparently when that light is on, the 12V system still runs from the main battery and not the little one. I drove from San Francisco to Seattle with that light on.
Does the Prius C main hybrid battery run the electrical starter for the hybrid gas engine then?
Yup, this little battery only turns on the electronics.
Wow, that is amazing, thank you for sharing!
with respect, why? also why such a small capacity on your Lithiums? VTC6s hold 5 times that.
I’ve got a ten year old prius, we’re still on the original big battery and maybe the original 12v too idk.
Lithium batteries are not safe. They can catch on fire. Lifepo4 doesn’t easily catch fire.
see i’m not well versed on the different types of lithium batteries. i figured LiFePO4 was just another lithium battery that had thermal runaway like the lithium cobalts and the lithium manganeses. TIL!
Can’t say I’ve seen cylindrical LIFEPO4 cells, I’d have said those were lithium-ion.
What BMS are you using?
I think they are A123 Chinese clones with battery hookup label. I wouldn’t trust them if they didn’t come from a reputable source LOL. I did test a few for charge discharge and it as a pack. But that was a while back. If I had gone with lithium only the pack would be a lot smaller. It’s incredible just how much power lithium chemistry can store.
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.
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.
I’ll have to take some pictures to send! LOL
My message is to just go with LifePO4. Its safe chemistry and it just lasts a lot longer than lead acid.
ldn’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.
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.
