Charging issues. Low voltage LiTime batteries

[sprinter99]

Charging issues.

I have a diy electric sailboat and my main battery bank is a diy 48v 280ah and works and charges fine. My backup bank is 4 -100ah litime that makes a 48v bank.

I checked the backup bank today and the voltage is 51.2v and it won't accept a charge. My victron mppt jumps at absorption and with a multimeter I see there is no amperage going to the batteries. Same thing with a lifepo4 charger (generator)

The individual litime reads
12.9
12.8
13.1
13.1

The two batteries are separated by a switch (batt1 and batt2 option) I can still use the backup bank for discharge so I assume it is not a connection issue

What could cause this and what should I do ?

Thank you!

 

[LakeHouse]

My first guess is that one of your batteries BMS's is cutting off charging. The SCC would see this as a voltage rise (so immediately switch from bulk to absorb) with no current flow, which could meet the tail current criteria and cause it to stop charging.
Your numbers don't quite add up there... The sum of those four voltages is 51.9V, not 51.2V. Even with some rounding on the numbers I wouldn't expect that much of a difference. Have you checked all of these voltage values with a multimeter?
How much current are you trying to push with the Victron SCC? On a sailboat I'm guessing this probably isn't the problem, but it might be worthwhile trying to charge with a very low current (say, 5 Amps), and then gradually increasing that value, all while monitoring the individual battery voltages.

In general, stringing four 12V LFP batteries in series isn't recommended, but with some monitoring and maintenance, it's not impossible for it to work, as long as the batteries have BMS's that are rated to disconnect the higher voltage.

 

[rodrick]

If you have a 12 volt charger try to charge each battery individually that way you can identify which battery is the problem

 

[mikefitz]

the voltage is 51.2v and it won't accept a charge.

One or more of the series batteries have entered protection mode. You may wake up the individual battery battery with a dumb charger or connect to an operational 12v battery to 'jump start' it.
A set of series batteries , each with its own BMS, will eventually get out of balance. Battery balancers are available to eliminate this issue.
Once you have individual operational 12v batteries, charge each fully before reconnecting in series.

Litime batteries often have poor balanced cells as supplied and operating is series may/ will not improve the situation.

https://www.amazon.com/Battery-Equalizer-Balancer-Supports-Trolling/dp/B0CLTZ2XQX/ref=sr_1_5?crid=1QA2PZM1UER8Z&keywords=Battery+balancer&qid=1703340491&sprefix=battery+balancer%2Caps%2C219&sr=8-5

 

[Gason]

This is due to the excessive unbalanced voltage difference in the internal resistance of each 12V battery. It may be better to fully charge each battery and let it rest for a while before connecting the battery packs in series.