Trolling motor battery question

[fishluvr]

In an attempt to increase the amp hours on my friend's boat we got four of the high capacity 6 volt golf cart batteries and linked them all up to get the 24 volts. So far haven't been real impressed/happy with the results. It seems like the motor isn't getting the thrust we used to get and it doesn't seem to last as long.

A rep from Minn Kota told us later not to use the 6 volt batteries.

Any ideas, experiences, options????
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