Having some battery issues and I could use some advice/help. I am pretty clueless about these things.

One of the batteries for my 36 volt Ultrex is not charging. It worked fine last week, but It can't get above 10.2 volts now. The battery is a year old flooded lead acid battery.

I have a Minn Kota charger built into the boat and the error code is: "the battery is less that 10.5 volts and the charger is in low power safety mode. Full charging will begin once the battery reaches 10.5 volts. If the battery does not rise above 10.5 volts, then make sure all loads are disconnected from the battery and try again."

I checked with a voltage meter and the battery is only 10 volts. The other 2 are fully charged.

Any ideas? I have let it trickle charge for 2 days and it's still only 10 volts. Do I just need to get a new battery? I checked the water levels and they are fine.

Also if I do get a new battery, can I get an AGM battery or for batteries in a 36 volt series all have to be exactly the same?

Thanks!

I had that same issue with a battery once and my solution was to connect it to my truck using jumper cables and letting it charger for 15 to 20 minutes (with the truck running). I then placed it back on my charger and it was above the turn on voltage for the charger. The charger then took over and restored it to normal. Be sure to check the water level. If you decide to get new batteries take at look at odyssey AGM batteries. They are pricy but you have an Ultrex so that should not be an issue.

All batteries in series should be the same in age and type if possible.

Check the water level in the battery, then give it a kick-start charge as indicated above, or connect a portable charger to it to get the voltage up then plug in your on-board charger to take over. Mine dropped all the way to 6 volts and I had to do this...

I would swap the battery charger banks so you are using one of the banks that has successfully charged one of the other battery's. That way you have eliminated the charger as the source of the problem. Check the water in the battery (only use deionized water) and that all terminals are tight and corrosion free. After that, I would take the battery to a parts store (Advanced Auto Parts) and have them test it.

Check the fuse going to the battery. My trolling motor battery charged the other day but my graphs didn�t because the fuse was bad.

First thing to do is check the voltage coming out of the bank to the battery to verify it�s actually charging. If not, check the fuse, if good then that bank is toast. If you don�t have a simple volt meter then hook the battery to one of the banks you know is good and see what happens.

If it is charging correctly then your battery is probably shot. You can try like some said above and see if you can get it above the low volt disconnect voltage but you�ve depleted it below it�s rated values so it�s likely not to last anyways. Do not ever mix battery types (lead-acid and AGM batteries). Get a load tester from wal mart or TSC and check the battery to see if it�s still any good. If not replace it. Continuing to use the 36VDC system with only 2 good batteries will deplete the other batteries faster than nominal discharge rates and you�ll be replacing all 3.

I would just take it to Auto Zone. They can tell you if a cell or more are bad. If so, badabing new battery right then and there. If not bad, they will give it a good full charge for free.

Thanks everyone for the help! I'm going to go get it tested tomorrow

Put a load tester on it. I suspect you have a bad cell.
If it is bad, go to Walmart and buy an EverStart MAXX. They come with a three year replacement warranty.

Cheapest route is just replace it with another wet cell like an everstart. If you decide to replace all 3, I suggest the Duracell AGM 31 series from Sam's club. $179 each but check periodically cause they will have them $20 off sometimes

I had one do the same thing. Checked the water level. Had to refill the water. Put on a 40 amp boost for about an hour, then charged it normally. Took 24 hours to fully charge. But haven�t had a problem since. That was about 4 months ago.

I took it to the autoparts store and they tested the battery and they couldn't even get a reading from it. He says it's dead.

Now i have to decide if i want to buy the exact same flooded lead acid battery or replace all 3 with AGM batteries. I already replaced my cranking battery with an AGM.

How bad is it to replace 1 battery in a series with a newer battery of the exact same type? Is it important that all 3 are the same age and quality?

If you want to spend the money, change them all. If not, move it around so your new battery is first in the series. I would still try to get a charge on it through the techniques above then re-test. The load testers don�t work below a certain charge either. It may still be salvageable...

the life of the new battery will be reduced if you put it in series with two older batteries

You might still get a decent amount of time out of it, but I would make sure to replace all 3 at the same time next time.

Have you tried putting a standalone charger on it? The autoparts store guys aren't always the sharpest dudes, they just tell you what the load tester says

yall were right. My cheap $20 battery charger I used to use on my old center console boat, charged the battery just fine, and now my very expensive 4 bank minn kota charger is working with it. I'm very confused as to why the minn kota would not charge it.