5 batteries one red.

[Hoohaa]

I have a bank of 5 * 12v batteries. They are around 3 years old.
Bought and installed at the same time.
Sit at around 13.7v.
I have been very happy with them.

While replacing my sink I was able to get a good look at 3 of them and noticed that the middle of the 3 was showing red in the little window.
I checked all of the voltages and they where all the same.
Do I need to disconnect the battery to test it properly?
Is it likely that the indicator window is malfunctioning?
Can it damage the other batteries in the bank?
Is it common for one battery to malfunction when wired as part of a bank like this?
Thanks. Jeff

[Chotu]

Yes. You need to disconnect the batteries to measure the voltages properly. Because they all affect each other in the bank.

[a64pilot]

Good Lord are they still made with that silly window?
That was a GM thing back in the 80’s when maintenance free batteries were just becoming a thing, it was a single cell hydrometer, and just about pretty useless.

I would say disconnect and let sit overnight, then check voltages.

[Pete7]

Certainly worth lifting them out and giving them a good clean including the terminals. If you can just route the wires so the pos and neg wires don't sit on top of each other that would be good too. You really don't want those rubbing together whilst you are sailing along.

Pete

[mickt243]

If you can get the vent cap covers off, step 1 is to check the fluid level and top off with distilled water.....

[Sailmonkey]

Originally Posted by a64pilot

Good Lord are they still made with that silly window?
That was a GM thing back in the 80’s when maintenance free batteries were just becoming a thing, it was a single cell hydrometer, and just about pretty useless.

I would say disconnect and let sit overnight, then check voltages.

That was a hydrometer? I always thought I’d was just an electrolyte level float.

Either way......borderline useless.

[S/V Illusion]

Three years old with that ‘magic eye’?.....
I haven’t seen that in many years.

[a64pilot]

Originally Posted by Sailmonkey

That was a hydrometer? I always thought I’d was just an electrolyte level float.

Either way......borderline useless.

It might have been, I’m not sure, only know what I was told, in that era the first thing I did when I got a vehicle was to get rid of the Delco battery, reason is they often leaked, and who wants a brand new car with paint eaten off of the battery area.

[a64pilot]

Originally Posted by Sailmonkey

That was a hydrometer? I always thought I’d was just an electrolyte level float.

Either way......borderline useless.

I did a little looking, apparently it’s been around since the 60’s, the first ones were actually part of the cell cap and may have been level indicators, however around 1980 or so it was part of the battery case of a maintenance free battery, and on the case it was labeled as a hydrometer.
Found this old commercial.
https://youtu.be/anL6BysEUT4

[Sailmonkey]

Originally Posted by a64pilot

I did a little looking, apparently it’s been around since the 60’s, the first ones were actually part of the cell cap and may have been level indicators, however around 1980 or so it was part of the battery case of a maintenance free battery, and on the case it was labeled as a hydrometer.

Found this old commercial.

https://youtu.be/anL6BysEUT4

Now that’s some fancy stuff

[Bill O]

Originally Posted by Hoohaa

I have a bank of 5 * 12v batteries. They are around 3 years old.
Bought and installed at the same time.
Sit at around 13.7v.
I have been very happy with them.

While replacing my sink I was able to get a good look at 3 of them and noticed that the middle of the 3 was showing red in the little window.
I checked all of the voltages and they where all the same.
Do I need to disconnect the battery to test it properly?
Is it likely that the indicator window is malfunctioning?
Can it damage the other batteries in the bank?
Is it common for one battery to malfunction when wired as part of a bank like this?
Thanks. Jeff
Attachment 213261

Have you ever added water to your batteries? Fairly certain those bigger panels do come up (need to gently pry them out) in those batteries. Kinda a misnomer that they are "maintenance free" since they aren't really sealed like an AGM. Sure they will last maybe 5 yrs before you need to replace them, but will last longer than 5 years if you add some water.

[dadster3]

You also need to put covers on the positive terminals.

[hlev00]

Not your question but something else to look into. There appears to be three grounds coming out of the box - two off the left end of the bank and one off the rightmost battery. There is only one positive coming off the bank. The multiple grounds might lead to a ground loop depending on where those all lead to. The two on the left might be okay if that post is acting as a branching point. The one on the right looks most suspicious. If it is in a circuit with a substantial amount of current, it is going to result in uneven battery usage.


The various gauges of wire in the bank at least make it difficult to assess if they are sized properly.

[Moontide]

Not sure what you mean by "sit at 13.7" Fully charged should be around 12.7. Is 13.7 with a battery charger or alternator active?

[SV__Grace]

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.