AGM Battery Issues

Sorry for the long post but try and stick with It there is a Lesson to be given or taken depending on where your coming from.

Have been having some issues with my Battery’s

Lets just start with the obvious problems first!

My Battery's didn't seem to be holding a charge like they used to. (they are 3-4 years old)
My battery charger is a (Xantrex True charge 60a 3 Bank charger) is a smart charger”
it has been cooking or Over charging "select" battery's.

I will try to explain. I’m putting my boat back together. I re-installed all 6 of my Battery's. (Sea volt Group 31 AGM 105AH) battery’s I have 3 banks of battery's.
Each bank has “2” of the Sea Volt AGM batteries. (See diagram) I noticed my Charger was not turning off. It always turn’s Off & On but after the initial charge it pretty much go's into sleep mode so it might turn on for a few min but the it would shut right off (typical float charge cycle) this happens when the batt’s are full. I got in the boat and felt one of my battery's and it was Hot as hell, I mean “Look out” this thing could have caught fire that hot! All the other batteries were fine As far as heat.

So I just assumed that I had ONE bad battery and that’s why it started getting hot and so I just bought a new one. And decided to keep a eye on it.

I put the new battery back in and the Battery charger started cooking another battery! So now my focus was on the Battery charger itself. I talked with customer support at Xantrex and they wanted me to test all my battery's b4 sending the charger back to them.
Brian at Liquid Trends in Modesto has a real nice "Snap On" battery charger/tester. He was able to test all my batteries. Ill post picks of the individual Test slips of all 6 battery's that shows what charger found out about each battery.

Brian had said that Normal internal impedance for an AGM is somewhere between 3& 5 MA. The new battery that I just bought had an Impedance of 3.88 MH. So that was a good base line for what the battery's internal resistance should be.

The older battery's had pretty high internal resistance. Ranging from 6 to 9 MA. This might be one of my problems. Now WHY is the question!

When I put my boat back together I decided to make some changes. I made it so that each bank had the exact same length of wire between battery's and all my runs are the exact same length. Both positive and negative. The idea was to keep the resistance different length wire can create all the same.

The second thing I did was to separate all 3 of my banks during shore charge sessions with solenoids. I have 3 banks they are all linked together as one. So the charger is NOT charging 3 individual banks like it should be charging. It’s charging one large bank because all battery’s are linked. So if I have a resistance problem or bad battery with one bank my charger could be working over time to bring back the bad battery to life and in the process Over charging my other battery's.

By adding solenoids I can break the 3 banks apart. When my key is in the off position. This will allow the charger to charge the banks individually. I could also add switches to control the solenoids independently so if I wanted I could charge 2 batteries or 4 batteries or all 6 at one time.

The advantages of having a charger with mutable banks are having the ability to charge banks individually.

My thinking is that with banks that contain 2 or more battery's and battery's are located in different locations spread over the boat the issue of bank #1 being drained more that the bank #2 and then all banks being charged as one could create problems.

When all the banks Are linked during charging the charger can't charge the lowest bank more or less because its NOT on a separate charge program it just throw’s a charge threw out the entire system and when the entire system reaches a state of charge the charger shuts off.

This could mean that if you have a week battery it could be leaning on a strong Battery to even the system out and in turn drag the whole system down. Because now one battery is doing the work of 2 or more.

I drew up a diagram of what I was doing. My wires run pretty much like this any way all I need to do is add the Solenoids.

So this concept address charging during the time being plugged into 110 or shore power but it doesn't address charging while the alternator is doing the work.

Another advantage of separating banks while charging it allows you to spot a problem right away. Most multi bank charges have a display that shows you the state of charge or current going to each bank. When everything is working well all banks should charge up pretty evenly and reach full state of charge around the same time. If you find your multi bank charger is working on one bank much longer then the other IMO this is your first sign of trouble.

Wanted to run this by you guys and get some thoughts.