I have a 2005 mercury xr-6 that I recently replaced the starter  battery for. I took out a deka battery that the dealer installed and replaced it with a bass pro shops brand that ( on paper ) was supposed to be more powerful  !! I was in a tx yesterday and started putting fish in the livewell at 8 A.M and by 10:30 my starter battery was dead. Fortunately there was enough power to supply my livewell pumps or I would really be upset. I was only running 1 gps/sonar unit too. Should I go back to the old brand ? Have any of you had similar problems with BPS batteries ?

Did you charge the battery when you got it?

Did you get a "starting" battery or a deep cycle battery?  Most fishing boats need a deep cycle battery to handle all those extra loads unless they have a separate house load battery so only the engine is on the starting battery.  Since the engines are relatively small compared to road vehicles, a deep cycle battery has no trouble starting them.

Starting batteries are designed to supply a high current for a short time which is rated as the CCA (Cold Cranking Amps) number.  This is nearly useless for fishing applications.

Deep cycle batteries are designed for low currents over a longer time which is rated in Amp-hours.  This is the number you need to use for selection.