question

Hi @CombatDiver

1. If you look at below LiFePO4 charging curve this might help understand my answer.

However the answer is no LiFePO4 cells do not have to be kept under 60% to extend their life. LiFePO4 voltages are relatively flat throughout charging/discharging cycle until close to the the very ends. ie close to 100% or close to 0%. At close to 100% the voltage then spikes (around 3.45v per cell you'll need to multiple this number by however many cells are in your battery, likely 4 if 12v system). Essentially a LiFePO4 battery wont be under any additional stress until the steep part of the charge curve (above 3.4v ish, people will debate on this number but around 3.4v if you're conservative up to 3.55v if not)

2. Given the answer is no to 1 then no need to worry on this question. However you're right if you wanted to do that you'd just set an upper limit using lower absorption/float voltage would be the way to do it. However no need given answer above.

3. I don't believe there is a way to set it based on SoC however setting a limit based on SoC wouldn't be ideal in my opinion especially for LiFePO4. Given to track SoC of LiFePO4 we have to count amps in vs amps out (unless we're at steep part of the curve ie 100% or 0%)

For lead acid the charge curve is relatively straight so voltage is a decent indicator for SoC ie if 12v = 0% SoC and 14v = 100% then in lead acid you could guess that 13v is 50% and you'd probably be close.

However for LiFePO4 isn't a straight line so it's hard to work our SoC from voltage alone without being at 100% or 0% (the steep part of the curve). Hence why smartshunts etc count amps in vs amps out.

If i use the graph below as an example at 20% SoC, the voltages looks to be around 3.25v and at 80% is around 3.3v, so it's so hard to tell SoC from voltage because it's so flat until the steep part of the curve. Therefore what most people will do is set their float/absorption voltages at the bottom of the sleep part of the curve. That way you're getting most energy out of the battery without stressing it too much with the higher voltage you would seen on the steep part of the curve.

Additionally looking at the graph for your first question. At 60% voltage is just below 3.3v so the battery isn't under any more stress that it is at 90%.

Hope this is useful. Let me know if you have any further questions. A really great resources for information and tests on LiFePO4 is a youtube channel called off-grid garage.

1. Unnecessary.

We have been fulltime travelling in our mororhome here in NZ for 9 years.

Our 4 cell 300Ah LiFePO4 Sinopoly battery has survived all those years with just a c4% capacity loss. In Ah from the original c315 to 302 last November. It both starts our 3.9l turbo diesel engine often multiple times a day and powers all our goodies.

I aim to keep the battery at 100% SOC but that never occurs in practice. Typically 100% by 2pm and 75% SOC at sunrise.

I suspect that those theoretical 50 to 80% numbers often bandied about are just that - theories.

Thanks to both guys!.

I shot the question, because I watch that with lithium is ok to do that, and some people stated in internet that it was the same for th LifePo4. Now Im fine

I have a second question. In my case, I will have full 100% all the days the LifePo4 set, almost always. And only at night I will be taking enegy for the batteries, but not too much. I guess most of the times, I will have discharges of 10% no more. So, I keep with this discharge profile, Do you think my batteries are going to last shorter?

Thanks BR

The battery may or may not last a few days or weeks less over its lifetime but you will NEVER know anyway. Insignificance comes to mind.

Just keep using your battery as usual. Fill it, use it and fill it again.

Surely that was the whole purpose of installing the battery anyway.

Enjoy it along with all all the advantages!

Something missing in this discussion is the BMS and cell balancing within the batteries. The BMS will only balance the cells when the battery is close to 100% charged. It's necessary to charge to 100% regularly. If this isn't done, out of balance cells can lead to premature battery failure.