Deep Cycle battery questions...

[Hillbilly_Hooker]

Please help this newbie boat owner...  I need to replace one of the two trolling motor batteries in my boat.  Today, an experienced boat owner told me to pay attention to the 'class' of batteries that I already have (i.e. are they size 27, 31, etc.) and not to mix one with another (i.e. don't have a 27 & 31 together).  As best I can determine, the 27, 31, or whatever, refers only to the size of the battery case.  If that is correct, does it really matter... is it ok to mix different sizes as long as both are deep cycle and not one deep cycle and one starting battery?

[Ben]

Basically, what it boils down to is:

Use deep cycle batteries for trolling motors

Deep cycle batteries are rated in Amp Hour capacity. The number of plates, is one of the main determing factors for AH capaticity. A group 31 can hold more plates than a group 27. That does not mean a particular group 31 battery has more, it's just the case can hold more. If you have a group 27 and a group 31 sitting side by side and they are both 115 AH batteries, the group 31 will usually have a longer life span than the 27. As the battery ages and the plates start to swell, (ever notice how the side of and old battery bulge out) they have more room in a 31 case to swell before they compress so much they short.

Unless you're doing some serious Tournament fishing or fishing big TM only lakes, two 105 - 115 AH group 27 batteries will give you all the run time you need. Group 27's are usually cheaper and easier to find.

As for mixing batteries, you don't want to use a lead acid and a gel cell. You don't want use a deep cycle and a cranking battery together. You don't want to use a two year old battery with a brand new battery.

It's not desirable to use two different brand batteries of the same size, or use batteries of the same brand with different AH capacities.

For the best runtime and battery life, always buy both batteries of the same make, size and AH capacity, at the same time. Never replace just one of a pair, unless that one died a very premature death.

I always check the date code on the battery. If it has been sitting on the shelf for several months, I won't buy it. It's very common to buy batteries in the spring a store had sitting on the shelf for six months, because they buy bunches and don't sell many through the winter. I've seen batteries at Wal-Mart seven moths old. That little brown and white round sticker on top is manufature date 8 04 means it was made in Aug 2004.  Some battery companies hide their's a little better and some code it, but you can always ask.

[Low_Budget_Hooker]

great post Ben, thanks.

[Hillbilly_Hooker]

Ben,

Thanks for a great post that answered all of my questions.

Robert