I took my trolling motor deep cycle out of my boat to put in my fishhouse. My boat has a 5 amp minnkota charger that always fully charges it. When I hooked it up to the 15amp minnkota charger in my wheelhouse, it won't fully charge. Its polarity is hooked up ok. Both chargers are multistage. Any thoughts?

Did you try the 15 amp charger on another battery to make sure it is working OK?

Is it a new battery? My understanding was they need to go through a number of partial discharges before they will accept a full charge.

Its a 3 year old battery. It has a pair that seemed to charge fine. When I get a chance I was going to see if that one battery needs its fluid topped off, and try switching banks and see if that makes a difference.

I always thought that higher power chargers are faster but puts less juice in the batteries...

How are you determining that the battery is or is not fully charged? By the charger? Using a volt meter? Specific gravity of the battery. If you are going by the amp meter on a battery charger it may be in error.

I was going to switch banks and see if that bank does the same thing on my other battery, if so , charger is going back. Will check voltage on digital voltometer.