LifePO4 Battery storage voltage

[Mac2]

I just read an article at Nordkyn Design by Eric Bretscher. Very informative. The article is about charging marine lithium battery banks and was very eye opening. My main takeaway was how I have been leaving my LifePO4 batteries stored while at the dock. I have 12volt and 24 volt systems. My house bank is 24 volt and is not being used at all while plugged into shore power. This means they can be sitting there for months not being used, or having the charger kick in at the same time daily (Float charge), creating a memory problem. Eric points out that the batteries will "degrade gradually when kept at full charge for extended periods of time and can develop memory issues when cycled inadequately". Contrary to my old way of thinking for lead acid batteries (full SOC), a low SOC is needed to preserve the LifePO4 batteries. He recommends 3.2 volts/cell, or 25.6 volts for a 24 volt battery. I was wondering if anyone else can confirm the above? I've can't find anything on my spec sheet for my batteries that refers to storage voltage. Storage temperature-yes. Voltage-no.

 

[tiltrider1]

What you state is what I understand. In my case, my batteries are like my generator, they are at my convince and convince is more important than longevity. Therefor my batteries are always charged and ready to go.

While I charge at 14.5 I float my batteries at 13.8. Fortunately, LiPo4 batteries have gotten cheap enough that I am really not concerned with a shorter life. Unlike L-16 or 8D batteries, I can easily replace my bank by myself.

 

[DDW]

Most of the literature suggests using a float voltage (if you must) somewhat lower than LA chemistry. However the tests I have seen on storage of LFP at full vs reduced charge suggests the resultant reduction in life is modest. A lot of literature suggests fully cycling an LFP a couple of times a year to delay the dreaded dendrites.

 

[Mac2]

Great points. The article does not mention how much they degrade, or how quickly they degrade (over time). As a liveaboard, it's not a hardship to turn my charger on the night before I plan on taking the boat out, so there is no reason for me to keep the batteries at full SOC.

 

[twistedtree]

Great points. The article does not mention how much they degrade, or how quickly they degrade (over time). As a liveaboard, it's not a hardship to turn my charger on the night before I plan on taking the boat out, so there is no reason for me to keep the batteries at full SOC.

I don't even worry about that since my alternator will bring the batteries back to full charge before I get to any anchorage, and that's when I care about having them full.

As for voltages, 3.45 to 3.5V will charge the batteries to 99% and leave plenty of margin to avoid pushing any individual cell over 3.6V. There is very little stored energy between 3.45vpc and 3.6vpc so you are giving up almost nothing by stopping the charger a bit on the early side.

That said, some manufacturers want a higher charge voltage to run their internal balancer. But I really have to scratch my head over guidance that calls for 3.6 to 3.65vpc as a routine charge protocol. That's right at the limit of damaging the batteries.

For storage, 3.30 to 3.35 vpc is fine. I have been using 3.35 vpc for years now. When you float them at that voltage, they settle in somewhere in the 50-70% SOC range.