Hi Shootandfish,
You have gotten a lot of good advice here so far! I am in agreement with your (and other's) assessment that AGM's are the best type of battery for your intended use.
Full disclosure; I don't own a trolling motor… or a boat for that matter. I also acknowledge that my opinions are biased due to the fact that I exclusively use Odyssey batteries in my truck (two Group 65's) and truck camper (three Group 31's)… However, I frequently operate high current appliances (microwave & air conditioner) for extended periods of time from my battery bank/inverter. I can say that I have abused the heck out of my Odysseys and after five years of use they continue to provide outstanding performance. They tolerate extremely high discharge current and have
no limit on bulk charge current (@ 14.7V). They are rated to 400 cycles at 80% DOD (same as NorthStar). Here is a link to their
Technical Manual.So, all that said; I strongly suggest that you include Sears DieHard Platinum (Group 31) batteries as part of your evaluation. The Platinums are re-badged Odysseys... made on the same production line at EnerSys and have the identical performance spec's. As an added benefit these batteries have a 36month free-replacement warranty and are stocked at Sears stores across the country in the event you ever needed a replacement.
As you already know, to get the best performance and long service life from AGM batteries you will need to have an appropriate charger… one that can provide high charge current and have the appropriate voltages for each stage of charging, as well as temperature compensation. Selecting a charger may prove to be an even bigger challenge (and more expensive!) than choosing which battery to buy. As a starting point I suggest that you take a look at the offerings from
KISAE and
Mastervolt.FWIW I use a ProSine 2.0 (no longer in production) which can charge at up to 100A and is highly configurable in terms of voltage, charge termination, and temp-comp. However, it doesn't sound like you're in the market for an inverter/charger.
I also own one West Marine SeaVolt Group 31 AGM (re-badged East-Penn/Deka) which I use in my travel trailer. Its performance has been just fine, no complaints at all. But to be honest I really haven't abused it at all since it is only used for lighting & running the water pump.
Good luck and please let us know what you finally decide to go with.
Cheers,
-Mark
