How to disconnect batteries safely

[Tbleppy]

I have 4 12v 100ah LiFeBo4 batteries( Amperetime brand ) hooked up 2s2p. They were running great until one day the solar array wasnt charging them due to a cable and the batteries ended up getting completely discharged. The problem was quickly fixed but the batteries are not operating at their optimum it seems. I want to use a multimeter to check them but should I do that when theyre all connected? I would like to know the steps which are taken to disconnect the batteries first from the system and then from eachother. I am assuming I disconnect the array using the breaker. Then I disconnect the charge controller using another breaker. Then i turn off the inverter. Then do I remove the parallel or the series connection first? Also, is this dangerous to do? Amperetime gave me directions on how to give them a boost. They said to discharge each battery individually. Then disconnect the load and let it sit for 12 hours. Reconnect the batteries in parallel and charge them up together. Let it sit for 12 hours. Reconnect to 2s2p. Then discharge to see if system performance has improved. Thanks for your help!

 

[MurphyGuy]

Turn off DC input to the charge controller coming from the solar panels.
Turn off inverter

Isolate both inverter and charge controller.

Disconnect positive and negative cables if needed.

After that, it doesn't matter which battery cables you disconnect or in what order, or if you even disconnect them.