Battery Question

[Tooeez]

The web is great for doing research, but I want to confirm with folks I trust (you guys) the info I found. Here's the issue: several years ago I replaced the dual voltage fridge with a 110v undercounter unit. Away from the dock it runs off a 2000 watt inverter. I have two group 27 batteries wired in parallel on the port side hooked to the inverter, two 27's on the starboard side with a selector switch that allows me to run the two stbd. batteries in parallel on the stbd engine, or put one on the stbd engine and the other in parallel with the two port batteries, or put all four together. When I first installed this setup I could spend 36 hours on the hook (using three batteries together) and still have enough juice to start the engine. About a year ago, after 12 or so hours of use, I started getting a low voltage alarm on the inverter when the fridge started (the alarm sounds when the voltage drops below 12). The run time before alarm got less and less, until now I get less than two hours before the alarm sounds.
The stbd batteries are 4 years old, the port bank 2 years old. With the engines running both banks show from 13.8 to 14.1 volts; once I shut down the port bank drops to 12.6, then within a few minutes (without any load) drops to about 12.3 or 12.4. The stbd bank is worse, settling in at 11.9 volts. Yesterday, after less than two hours on the hook, the port batteries dropped to 11.3 volts when the fridge tried to start, then rose under load to 12.1 to 12.2. When the load stopped the voltage went to 12.4.
I realize this is a lot of info for this simple question: the web says voltage drop under load is most likely caused by sulfated plates in the batteries. Does this seem right, or can there be another issue here I should check before I replace the batteries? I find it puzzling that both starters spin at normal speed, even with the low readings on the volt meters.
PS: all the connections are clean and tight.

[ranjr13]

I'd start by load testing batteries individually. If one has a bad cell, it will adversely affect the rest of that battery and any that it is connected to. Fully charge them, then completely disconnect them and test using a good load tester one by one. If they all fail, they all may be ready for the battery graveyard. You lose efficiency by inverting voltage, so it's going to draw more doing it the way you have setup. I run 12v only, and if I need to keep it cool at the dock, the batteries are being trickled. Otherwise the batteries are only charged when running so they're not overcharged. Gel batteries last longer under harder cycles - that may be an option for your setup. That would be my plan. Good luck.

[Tony Meola]

If you don't have a lady ester take them to Auto zone, they will load test them.

As was said you could have one bad battery or two or more. Batteries go bad and even new ones die. First off stick with a good name brand. I just put in Deka after getting 8 years out of Interstate truck batteries group 31.

I don't have an inverter.

Are you running 4 batteries or 6 batteries? Was not sure. I run 5. Two to start each engine and one house.

What type of onboard battery charger do you have? Does it step charge the battery banks?

If you charge a battery and in 30 Minutes it drops under 12.5 volts, with no draw on it
like yours to 11 volts, your battery is probably toast.

When my batteries quit on me, I noticed they were taking a little longer to come up to a full charge and then this winter they stopped taking a charge completly.



If I was setting it up, I would a start battery for each engine and two house. When starting the engines using both start batteries will extend the life of the start batteries.

I would set it up so if needed you can bring all 4 on line to start an engine. To be safe the start batteries should be isolated from the house except in an emergency. You may need an ACR to make the work.

I am a little crazy with my batteries. I pull them for the winter, charge them with a smart charger then set them on a flat/maintence charger for the winter. In the spring just before putting them back in, they go back on the smart charger up to a full top off then I desulfate them. The charger is made to do that.

I figure 8 years is worth the trouble.

I think Bob has close to 15 years on his AGM's.

[bob lico]

my batteries are two from 2005 and two from 2006 in continuous use with every conceivable electrical,electronic devise possible ,all kind of games on flat screen for grandchildren as well as micro,a/c, heating,blender,coffee,refrigerator,electric toilet,Fussion stereo,all kinds of fishing lights,underwater,cockpit,bridge ,million watt spot, odassey 2150s AGM. batteries

[JohnV8r]

My 4 Group 31 AGM batteries (2 starboard/2 port) are from 2008 and still going strong as well. Starboard batteries start starboard engine and handle house load.

Port batteries handle port engine and have a parallel switch in the event I run the starboard batteries down too low.

I always replace both batteries on either bank when that bank starts to give me low voltage or won't hold a charge. I replaced three banks of lead acid batteries (2 starboard and 1 port) in five seasons before switching to AGM. I have not replaced either bank since switching to AGM.

I also updated my charger to handle AGM at the same time.

[Tony Meola]

One other thing, even though they may say maintence free that is not quiet true. Unless the are really sealed so you can't open them they may need water. Use distilled only.

[Carl]

You mention Group 27 Batteries...but are they Deep Cycle Batteries?

If your starting engines with them...I'm thinking you have Starting or Dual purpose batteries.

When I first hooked up my inverter I killed a few batteries on the hook. A couple deep draws and those batteries never fully recovered...try boiling a large container of water in a Microwave. Then I switched to Deep Cycle House batteries for inverter with starting batteries for motors. Setup that way I got a good few years out of them...slow to recharge, but they did recharge time and time again.

[Tooeez]

Thanks to everyone for all the input. I realize I made a couple of mistakes along the way. For the last 30 years I used Sears Diehard deep cycle batteries, and got about 8 years out of them, even with the old 12v fridge or the inverter draining them flat on a regular basis. Two years ago when I replaced the port bank Sears was out of stock and I was moving and could not wait, so I bought 2 Interstate group 29 deep cycles. They are the ones that started giving me trouble within a year, I think now mainly because I mixed different capacity batteries together: the Diehards are 105ah and the Interstates only 87ah. I have also learned that deep cycle batteries should be charged with a mulit-step smart charger for the best results. My original equipment charger is not very smart, and only has two steps: on and off. So the plan is to replace the charger with a 2 bank smart charger, and then swap out all four existing batteries for four group 31 deep cycles.

[JohnV8r]

I think you will be pleasantly surprised at the value you get with AGM batteries, despite the extra initial expense. Mine have taken A LOT of abuse and are still performing WAY BEYOND my expectations.