Keeping Your Trolling Motor Batteries Charged
May 7, 2003
The Bottom Line Charge your battery ASAP. Check battery water levels once a month. Store batteries in a cool dry area during periods of little use and maintain with a trickle charger.
How to charge your trolling batteries at home.
Normally, deep cycle batteries do not require special charging procedures. However, most manufacturers recommended that you use a charger designed specifically for deep cycle batteries. It is best to slow charge all batteries, especially deep cycle. The 20% rule should be used when charging a deep cycle battery. That means to choose a charger where the maximum current (in amps) is less than 20% of the Ah rating. For example, an Interstate SRM-27 is rated at approximately 100 Ah, so a 20-amp charger should be the maximum. Also, it is best to use a charger that is adequate to recharge the battery within 10-12 hours. During periods of little use I like to maintain the charge with a trickle charger.
Traditional battery isolators require you to modify the electrical wiring in your outboard to get to the alternator output. This involves extra cables to the engine and often voids your warranty. Battery isolators also have a built in voltage drop so now your starting battery and your trolling battery no longer get a full charge.
There is now a simple hookup that anyone can do. Just connect a West Marine Combiner 50 between the starting battery and the trolling battery. Whenever the outboard engine is running, the green light on the combiner will indicate when it has connected to the trolling battery to share the charge. When the engine is off, the green light will go out indicating that the batteries are isolated so the trolling motor won't run down the starting battery.
Obviously, the ability of the alternator in the outboard engine to keep the trolling battery charged is dependent on the size of the alternator and how long the outboard engine is running in relation to how long the trolling motor is running. You only get a complete charge when you have made long runs with larger outboards, but it does really help extend the length of time you can run your trolling motor during the course of a day. This is really important for bass tournament anglers!