Lead Acid to LiFePO4 conversion

[Kzneft]

I can't find a conversion so thought I would ask. My RV has two 6-volt Lead Acid batteries in series to get 12v. Says on each batter it's 225 Ah @ 20hr. So how many 100 Ah Lithium batteries am I going to need? I doubt I would just divide 450 by 100, so thought I would ask.

 

[FilterGuy]

When wired in series, the voltage adds but the Ah stays the same so you have 225Ah of lead acid batteries. Even deep cycle lead acid should not be drained below ~50% so your usable AH is ~225 x .5 = 112.5Ah. Consequently one 100Ah Lithium "drop-in" batteries will be close to what you have now. Two would be a lot more than you have now.

Note: I am talking about *batteries* not cells that you would use to make a battery. (A 12 volt LiFePO4 battery will have at least 4 cells)

 

[soylentgreen]

Agree. Not only will one 100Ah Lifepo have roughly equivalent energy (*) it will have better power (voltage is higher, and doesn't sag as much under load) and is more efficient at charging back up: lead acid requires a long "absorb" time which is inefficient, whereas LFP is mostly "bulk".

If you have the space and can afford it, get 2 x 12V lithiums and wire them in parallel, and your system will be much better than before. (And probably cheaper, in the long run, since LFPs tend to last forever).

* the one situation where a 225AH lead acid battery might beat a 100AH lithium is in a very low amp draw, which isn't very relevant for RVing.

 

[John Frum]

Also LFP has negligible peukert effect.

Peukert's law - Wikipedia

en.wikipedia.org