Can I swap my 12 volt battery for a lithium jumpstart module?

I'm getting tired of paying outrageous sums of $$$ when my 12-volt battery needs replacement. Can I just swap it for one of those $50 lithium-ion jumpstart modules instead?

My first replacement was a dealer battery for $140 because I ran it dead sitting in my driveway listening to the radio with the engine off. Five years after that I went with the Optima from Amazon (not a perfect fit, but not too bad) for $130 and a 3-year no-questions-asked warranty. That came in handy when we spent the winter in Florida (the Prius was in Michigan in a brutally cold winter, even with the SmartKey system off). The battery read 0.3 volts when we returned and never did take a proper charge. Amazon swapped it pronto, no charge.

Now the same battery goes for $240 because they know they can get it. This is getting old. And I know I'm going to have to buy one or two more eventually. If this idea works, it could be a dramatic boon for all Prius drivers.

Can I just swap in one of those lithium battery packs (generally made up of 18650 cells and weighing about 40 pounds less than the OEM) that are usually used to jump-start any car? My understanding is that the only thing the 12 volt battery does is run the computers (which enables the car to start) and the horn, heater fan, lamps (not the HID headlights) and as long as the car is running, the traction battery and circuitry constantly charges that system, anyway.

What I don't know is whether the car's 12 volt charging system would be damaged by this change, or whether the lithium batteries would protest / blow up (no fun at all), not play nicely with my winter-long $10 car trickle charger, etc. These modules typically get charged slowly with a 5-volt phone charger, not the 12 volts from a car.

I've seen a few Youtube videos of young reckless fellows swapping their 12 volt battery for a stack of lithium cells, and they claim it's one of the best things they've ever done. Even if I have to make my own pack because the jumpstarts won't charge that way would be reasonable.

If I work up the nerve to try it, I expect that monitoring the temperature of the module would be a good place to start. I've read that it's bad form to connect two large batteries in parallel without a monitoring system, or the higher-voltage battery will constantly try to charge the lower-voltage battery. And the connector swap is certainly not a show-stopper for most shade-tree mechanics.

Any ideas?

 

After some more research, I've learned this: LiFePo4 batteries (Lithium Poly -- thank you very much @fmerkel)) are available from minor vendors you never heard of for around $350 and they seem to have all the features I'd want. Their target market is racers who want to save some weight and not worry about their battery. No venting needed, an additional "backup" cell inside (whatever that is), and no possibility of a fire or leaking crud in a rear-end collision. Link to eBay

I also read a post from a fellow who installed a $50 garden tractor battery from Walmart, and he's quite happy with it. The terminals aren't a match and require a little field engineering. Terminals are cheap, but I think he might have drilled some holes and used some screws. This might be a little tricky to explain to a dealer when trading in the car.

I asked my local library to interloan a book for me, "DIY Lithium Batteries: How to Build Your Own Battery Packs" by Micah Toll. There are some critical details about wiring, charging and controllers to keep Lithium-Ion and Lithium Poly packs safe. The outlaws I saw on Youtube seemed a little too cowboy for my tastes. I want "reliable long life" more than I want "cheap and risky."

FWIW, the Optima "replacement" number is 8171-767 while the generic number is DS46B24R (Amazon and elsewhere, $240). They seem to be just a smidge bigger than the OEM, but that shouldn't stop you. There's a plastic carrying strap that will likely have to be removed, isn't typically shown in the photos, and comes in handy when wrestling it into place. It's a little clumsy to remove the strap once the battery is in place in the car.

Bottom line -- It seems entirely possible to replace the OEM battery with a superior battery, whether it's the Optima yellow or a Chinese Li-Po. Both are more expensive, both should last longer, especially in very hot or cold climates. You can't get the Li-Po wet, so marine use is out, and a fire on a boat from a Lithium-Ion is far more serious than a fire on land. You can't run from a burning boat.

Slapping together some old 18650's that I scavenged out of the Lowe's recycle cabinet or peeled out of discarded laptop battery packs remains to be seen, largely for the fire issue. Lithium cells are extremely powerful. One advantage I have is that I at least own a decent battery charger for individual 18650 cells. From eBay / China for around $25, it tells me which cells are the strongest and which ones are flaky. I just write the capacity on the side with a marker. eBay link for Liitokala charger. In the meantime, I'll probably just keep using my old 18650's for the super powerful flashlights I get on eBay since the cells they usually sell with them are junk.

 

Thank you, @fmerkel for straightening out the terms; I was careless.

I've found that reusing 18650's entails removing the welded strap conductors. I tear the strap off with a pair of pliers (being careful not to abuse the insulation at the edge of the cell -- a dead short) then remove the four remaining nubs with a cone-shaped grinding stone on a Dremel tool. If I see cells for sale that have absurd ratings (anything above 3300 mAH or weighing less than 42 grams) I know they're fake.

 

@TMR-JWAP Thanks for the follow-up. I think you're right.

This started out looking for a $50 fix and ends up being a textbook case of negligence (which insurance companies never cover, BTW). I guess I got pissy when Amazon's supplier doubled the price of the Optima for no reason other than "they can."

Looks like I need to stop trying to be so cheap and just consider it the cost of doing business. I did learn about LiFePO4's along the way, thanks to @fmerkel . . .