12V Lithium

Anyone feeling the winter crazy's and in need of a 12v, Battery Hookup has an "interesting" possible replacement.

LithiumPower 12.8v 32ah 410wh LifePo4 Module w/ BMS – Battery Hookup

Should work,especially if the BMS is as good as they claim. 32A (1C) discharge should be enough - as long as there's a little wiggle room - worst case it would need a capacitor for the very short transients at startup. Of course, it might not work, or it may not fit or...

If we could reliably demonstrate that this style of lithium is a good replacement for the expensive and fairly low capacity lead acid we could potentially save some money and have a better battery for our cars. But that's not where we are, so if you go this route it's very much experimental.

I'd buy one, but I've just (last week) replaced with a very similar, but new-and-much-more-of-a-pain-to-install (tiny terminals) 30ah lithium (40A discharge, designed for solar storage, a little more expensive). Not enough miles or time yet to know how it's going to work out...

 

I don't know the answer to this. The limit is likely the BMS not the cells - those should be able to take higher charging currents. Discharging, I would expect the BMS to drop out if you pull too much current (it does on smaller BMS systems) but I don't know the behavior when charging.

I'm surprised the the DC-DC doesn't have any regulation to the battery charging system. It's not advisable to charge lead acid at much more than 1C and the recommended rate is usually somewhere less then 0.5C.

 

Replacing with a true "starter" battery will be much more expensive, although should work without issue. The BMS for a starter has to provide 400A+ to start a car. I would expect the low-cost, low amp lithium to be a suitable replacement in the Prius. The cost has recently come down enough for me to feel it's worth testing.

The Lithium battery was much smaller. The issue with fit was to raise it up enough for the connections to reach. It also has tiny terminals so I had to shim the connectors to get them tight.

I did think of using something similar in a minivan with the idea of bypassing the BMS with a high-amp contactor when the starter is engaged. Considerable effort to wire and without some cleverness you could still over-discharge the lithium while starting - the work didn't seem worthwhile. My motivation in that case was that, with all the work-from-home, that van has driven almost no miles and the battery has discharged and destroyed itself (I bought another LA and a battery disconnect).

 

The lithium has been in the car for a little over a year now. The car doesn't get driven much - part of the motivation was to get a battery that would cut out before a damaging over-discharge.

So far I have not noticed any appreciable difference from the Pb. I don't track it that closely, but the MPG seems to have increased slightly, but that could be confirmation bias or just a result of putting any good 12V in the car.

Battery Hookup has these batteries in new condition, but somehow only in pairs...
https://batteryhookup.com/products/new-2-pack-li-age-12-8v-32ah-410wh-lifepo4-w-bms?variant=41203476594850

32A should be enough, but see the comments above and reach your own conclusion.

 

Two year update. Still going fine. One time the car was left for long enough that the BMS kicked out and saved the battery. You then need to apply 12V to get the car rolling and charging again, but the battery is find (unlike lead acid which, without a BMS, would discharge to zero) That was only once and the car routinely sits for a month or so without a problem.

Haven't noticed any real difference in the car and have mostly forgotten that it has this odd little lithium rather than the recommended lead acid.

 

Battery in the second Prius (2006) died. I replaced with a different brand of LiFePO4 12V 36Ah - Pionergy - $130 . Very shortly after installing, the combo-meter went out - the standard problem needing the capacitor replacement. Possibly related to the battery change and so a higher voltage, but probably didn't matter whether Lead Acid or Lithium.

The biggest challenge in using these batteries is the tiny terminal sizes on the lithium batteries. For this conversion I created a battery "post" for the positive side using a 3/8th copper pipe cap. Drill a hole in the bottom for the terminal screw, clamp the terminal clamp around the copper cap - it's about the right size - screw into the battery through the hole in the bottom. The negative clamp is smaller and this time I just screwed the clamp directly to the battery terminal (seems to make good contact).