Forum Discussion

timelinex's avatar
timelinex
Explorer
Oct 08, 2023

Lifepo4 battery charging confusion

I bought 2 Lossigy 100ah batteries and replaced the converter on my 2021 Grand Design 381m with a 60a powermax pm4. So far so good. The Powermax charges at around 40a, which is 20a a piece and the advertised amount to maximize longevity. I'm having a hard time working through what is the right setup for me

To clarify MY goals...I have done alot of reading and know the conservative options are "better", but dont know what that actually looks like in real life. I dont go super often. I obviously want to get a good life span out of my batteries, but if I get 5 years instead of 10, by being more aggressive towards convenience...then that's a good option. But 2 years would not be acceptable. So keep that in mind when answering my questions!

1. The PM4 has 3 stage option or flat voltage. I set it at a flat voltage of 14.4 as I read somewhere to do that for lifepo4. But my concern is that the voltage remains at that even when it's fully charged. I thought I read that's not good. Is the 3 stage better, as it has a float? I do imagine it's a slower charge though, which is a bad outcome...

2. If doing a straight voltage, is 14.4 the right voltage? I asked the company and they just said anything under 14.6 is fine. I dont think it's their engineers answer questions....

3. I know the 40a it is currently charging at it optimal....but I would really prefer faster so I have to run my generator for shorter periods to recharge when boondocking. It's not just a fuel cost issue, but rather noise and disturbance one. I read the 75a one does about 55amps for people. How much worse is it for the batteries to charge at 30a vs 20a? 100a one (40a each?) would be even better, but im guessing that will start pushing things...

It would also be a good thing to have a stronger charger if I decide to add more batteries. Then I won't need to waste money on upgrading the charger.

Thanks guys!
  • Tango424's avatar
    Tango424
    Explorer III
    Jan 17, 2025

    Ok ow I'm a bit late to the game but check out a guy on YouTube

    Will Prowse  he has the answers you're looking for 

  • StirCrazy's avatar
    StirCrazy
    Moderator
    Oct 11, 2023
    ScottG wrote:


    I think you meant 4000 cycles there right?


    haha ya , thanks I'll fix that
  • 3_tons's avatar
    3_tons
    Explorer III
    Oct 09, 2023
    For the uninitiated, Solacity.com has a fairly decent primer on the subject:

    https://www.solacity.com/how-to-keep-lifepo4-lithium-ion-batteries-happy/

    3 tons
  • ScottG's avatar
    ScottG
    Nomad
    Oct 09, 2023
    StirCrazy wrote:
    So, a couple things here. I just looked up your converter and no it's not made for Li, but it will work, kind of as you can set a single voltage. Yes, setting for 14.4 would be good for charging but if you stay plugged in for any length of time, I would want a way to disconnect the batteries, so they are not held at 14.4 for longer periods of time.

    Ideally you would have a two staged converter that has the main charge at 14.4, then a float of about 13.6V or even a bit lower.

    I also looked up the batteries and they say the standard charge current is 40amps per battery and a max of 100amps per battery, so you could have went with a larger unit. The only time you're going to hurt the battery by charging it is if the battery gets too hot while you're charging it. but it also works if you are under the standard, won't increase the life at all just ensure the temp build up is lower.

    second (not for the original poster), I am not sure where this idea of basing the life of a LFP battery over time instead of cycles is starting to creep in from, but it only works out for a cycle life of 3650 and a full cycle every day for 10 years. It isn't really a good way to measure life as how many people fully cycle your battery every day. Also, every battery generation comes out with a different cycle life. The new cells I have on order say 4000 at the 25C standard, and if you operate between 10 and 90% instead of 0 to 100 they raise it to 6000 cycles. So instead of using 10 years to 80% let's try stick to the true definition of cycle life which is the number of cycles (defined as 100% to 0% and back to 100% ) that it will take to reduce the battery to 80% of its initial capacity. So, for instance, my new batteries are eve 304Ah cells which quite commonly will put out up to 320AH new. So, if that is what I get on a capacity test, I would expect after 400 cycles if I used all 100% of the capacity that I would have 256AH left and still have a perfectly usable battery, just somewhat smaller. I doubt I would ever reach the cycle life of the battery in my current way of using them.


    I think you meant 4000 cycles there right?
  • StirCrazy's avatar
    StirCrazy
    Moderator
    Oct 09, 2023
    So, a couple things here. I just looked up your converter and no it's not made for Li, but it will work, kind of as you can set a single voltage. Yes, setting for 14.4 would be good for charging but if you stay plugged in for any length of time, I would want a way to disconnect the batteries, so they are not held at 14.4 for longer periods of time.

    Ideally you would have a two staged converter that has the main charge at 14.4, then a float of about 13.6V or even a bit lower.

    I also looked up the batteries and they say the standard charge current is 40amps per battery and a max of 100amps per battery, so you could have went with a larger unit. The only time you're going to hurt the battery by charging it is if the battery gets too hot while you're charging it. but it also works if you are under the standard, won't increase the life at all just ensure the temp build up is lower.

    second (not for the original poster), I am not sure where this idea of basing the life of a LFP battery over time instead of cycles is starting to creep in from, but it only works out for a cycle life of 3650 and a full cycle every day for 10 years. It isn't really a good way to measure life as how many people fully cycle your battery every day. Also, every battery generation comes out with a different cycle life. The new cells I have on order say 4000 at the 25C standard, and if you operate between 10 and 90% instead of 0 to 100 they raise it to 6000 cycles. So instead of using 10 years to 80% let's try stick to the true definition of cycle life which is the number of cycles (defined as 100% to 0% and back to 100% ) that it will take to reduce the battery to 80% of its initial capacity. So, for instance, my new batteries are eve 304Ah cells which quite commonly will put out up to 320AH new. So, if that is what I get on a capacity test, I would expect after 4000 cycles if I used all 100% of the capacity that I would have 256AH left and still have a perfectly usable battery, just somewhat smaller. I doubt I would ever reach the cycle life of the battery in my current way of using them.
  • CA_Traveler's avatar
    CA_Traveler
    Explorer III
    Oct 09, 2023
    Flooded battery charging is completely different than lithium. While a 3 stage charger can charge lithium it may not be the best for you. Lithium can take a full charge until the amps drop to 3% and then the charger should shut down, checking to see if additional charging is needed.

    Maximum rate charging means less time and that can be beneficial for gen or solar based charging. Pedestal charging may not be a time factor.

    Of course lithium batteries can be discharged deeper w/o issues but then that power needs to be restored. But nice to have that option.
  • ScottG's avatar
    ScottG
    Nomad
    Oct 09, 2023
    If you work your batteries hard and fully discharge/charge them every day, after ten years they'll still have 80% of their capacity.
    So you don't have to be nice to them in that regard.
  • Cptnvideo's avatar
    Cptnvideo
    Nomad
    Oct 09, 2023
    We have 5 206ah SOK LFP batteries that are only charged via solar & MPPT controller. My OEM converter is unplugged.
    My settings are 14.2 volts bulk charge, then 20 minutes on absorb charge, same voltage, then float at 13.6 volts.
    My MPPT controller has and will put out 100 amps which would be 20 amps per battery. Obviously, that output varies by time of day and season.
    You don't have to fully charge LFP batteries nor do you have to charge at the 50% discharged point like flooded batteries. So this gives you a lot of flexibility when running the generator.
    Answers here concerning the voltage settings will vary quite a bit. I gave you my opinion.
    A little off topic, but you mentioned knowing not to run large loads off your batteries/inverter. We run an A/C unit (off solar & batteries) in the RV while traveling. Our drives typically are 3 hours or less. So you can run large loads IF your inverter and battery bank are sufficiently sized.

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