I recently encountered a similar situation with my AGM
battery bank and while I'm no expert, I've learned a few things that I'll share.
Yes, definitely check the electrolyte levels on these batteries. Assuming that isn't the problem, next step is to check the voltage of each battery and to do so you must disconnect the batteries from each other and the boat
. Then let them sit overnight, disconnected and test again. Great time to do maintenance such as cleaning
, inspecting connections, etc. A battery that is bad or deteriorating will have lower voltage than the others and will typically lose more overnight than the others.
One bad battery can mess up the performance of your bank. Here's my experience of that:
Two years ago, to prepare for our current
lifestyle as full time cruisers, we completed the refit
of our boat
, which included a battery bank of six high quality 6V Mastervolt AGMs. Total capacity 1200amh. Installed and recommended by our electrician, who is a wiz and I trust him.
Fast forward to earlier this year we were getting low voltage alarms going off when the battery monitor
was showing 78%. It didn't make sense that our battery bank would be at 10.2 volts having used only 1/4 of capacity.
Testing as above found 1 battery testing lower voltage than the others. Following the instructions of my electrician I ended up disconnecting the battery pair with the suspect battery.
So now my battery bank is 800amh but performing as it should with no more low voltage alarms. I can go longer and use more battery capacity between charges, and the bank charges with the generator
and reaches 100% much faster than before.
The bummer is that if one battery in a bank goes bad, the entire bank must be replaced. The good news is that the price
of lithium batteries is going down and in a year or two we'll go that route