Drop in 12v LFePO4 battery in a Gen 5 Prius Prime

probably nothing, it’s worked in older generations

 

Lighter wallet

 

This is the first time I've read about the possibility that the Prius 12 volt charging system might pump more current into the 12 volt battery than it could handle, whatever chem that battery might be.

I personally think Toyota programmed the 12 volt system to charge the battery at a really low amperage. Way lower than any car using an alternator, at least any that I've owned.
But until we get somebody to actually get Amp readings across a full spectrum of use cases, we wouldn't know for sure exactly how many amps the charging system actually hits the battery with at any one time.

 

Disregard, misread

 

I'd love to know how to get accurate internal resistance reads from batteries while both discharging and charging, since most times I read about it, I see only one reading and not too much else about when the reading was taken or under what ambient conditions the battery was exposed to.
Anyways, here's a chart for 12 volt lead acid and a few other chems.
Battery Internal Resistance Chart | Battery Tools
Again, the chart is a basic generalization for what healthy batteries should look like under ideal conditions and at nominal voltage.
Take from that what you may.

 

So has anyone actually tried this? I recently replaced my SLA with a LiFePO4 in a UPS. I was surprised to see it cut off at a much lower load than my SLA. The problem is the BMS. While an SLA can provide surge current, the BMS will simply shutoff at its rated amps. I'd hate to learn that the BMS couldn't take the drain or charge current while you're on the road! In my case it was a 6AH battery with a 6AH BMS so it's a pretty low limit. You'd probably have to go with something like a 100AH battery with a 100AH BMS in which case probably nothing would knock it off its feet but then you're talking $200 which is a lot more than a lead acid... still probably cheaper than a gel/SLA and save you money in the long run. But it's curious if this was a good idea, why wouldn't Toyota have done it? A LiFePO4 weighs a fraction of the Lead Acid. How much money do they put into each car to just save a few pounds?

 

Dealership price of a replacement Toyota TrueStart lead acid battery that fits the gen 5 Prius is $206 (before discounts, can be found for cheaper depending on the dealership).

00544-H4052-470 - Truestart H4 (En) Longo Toyota Parts

Truestart H4 (En) 00544-H4470-TS | Parts Molle Toyota

 

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