Bad Battery Troubleshoot


I’m hoping to get some advice or insight on my problem.
I have a 2008 Gem elxd and it has nine 8v deep cycle gel batteries. I bought it in early 2017 and it’s been working great with the set of batteries that it came with (Manufactured Dec 2013)! Last time it got used was 8 months ago in October 2018 and while it’s been sitting in storage I’ve had the battery disconnect switch turned to off for most of this time period, except every other month when I plug it in to keep it charged.

I tried to drive it last week and the charge went from full to one red bar and it barely made it 100ft before losing power. I checked the voltage on all the batteries individually and they all read around 8.4v-8.5v except one which read 7.5v and I’m suspecting it is the culprit.

Is it possible that this one undercharged battery can be recharged individually and then function properly again or has it most likely failed and needs replacement?

Can I replace the one bad battery and regain close to normal range and capacity again?

Thanks in advance for your help!

you can try and individually charge it but it probably has a bad cell . If your other batteries are still in good shape you can change just one . It is not the proper way to do it but it $2,000 less :upside_down_face: