Battery question

[O]

I have two 12 volt batteries hooked up in tandem to power a 24volt trolling motor. It was dead this weekend after sitting for a month or so without use. I charged up one of them but the meter on the charger would not go past 50% charged. The battery has water at the normal level.  I am not sure of the age of the batteries, just purchased the boat at the beginning of the summer.
Is it time for new batteries?

[stripernut]

The really bad news is that you should replace both batteries at the same time. I know many people don't do this, but is is the way it should be done for many reasons. When running batteries in series (24 volt or more) or in parallel for 12 volt it is important that the batteries be the same size, type and age and even better if you get them in the same lot number. With out going into a lot of detail they need to be "balanced" as much as possible, your system will last longer, not damage your electrical equipment, charge faster and run better. 
Will it work if you don't, yes, but the odds of things going wrong go way up and it shortens the lives of the batteries...
Tight Lines

[smokey]

The charger wouldn't go past 50% or the battery wouldn't go past 50%? My charger won't go past 75% no matter how long I charge it. And then I unplug it and plug it back in and it will be at 100%

Just something to think about.

[Jethro]

Do not forget that most deep cycle batteries are really only good for no more than 300 cycles. And those are the really good batteries.