One 6V battery discharging really fast

RichieW13 wrote:
Almost 3 years ago I swapped out my 12V battery for two 6V (Trojan T-105) batteries.

Last weekend, I noticed that my trailer was losing power really fast after charging up. I used a volt meter and discovered that one battery was reading ~4 volts and the other was reading ~6 volts.

The water level looks to be fine on both.

Is it possible that one battery is just bad? Is there some other issue I should look for? Should I just replace the bad battery, or do I need to replace both to keep them approximately the same age?

No mention of an hydrometer!!!!

Absolutely must dip an hydrometer into all six cells to know what is really going on.

Say you are into the green on all three of one batt, but only on two in the other batt. Now you must decide whether to to get one new 6 or two new ones.

IMO it would depend on how many cycles the "good" battery has done and what its SG is on the three cells. If almost as good as new I would keep it and get one new one. Or if not, not.