While out fishing today, I was running my modest radio, a Garmin 5” plotter/FF, and a new Minn Kota 55LB trolling motor. When I set the TM to full speed it caused my Garmin to display a low voltage message, voltage below 10.7 volts. When I set the TM to a speed that was one step lower than full, the alarm would go away. This happened right when I got on the water. My boat is configured with a starting batt which only runs the engine and a house batt that runs all else (including electronics, lights, radio, trolling motor, etc.). I just tested the voltage on the house batt and it reads 12.59/12.6. This is 5 hours after getting off the water. I have a 17’ length of 4 gauge cable running to the TM, so that should be fine. Battery is a Walmart Everstart G29 battery that is 3 yrs old but has been maintained. Fluid is levels are good and I have used a battery minder charger on it.

Hoping one of our resident guru’s can tell me how I should go about chasing down this gremlin... my first inclination is to buy a new battery but if possible I’d like to know how to determine what the cause is before spending the money.

Putting a large load on the battery is going to pull down its voltage. If you want to get technical its called internal resistance of the battery but is technically the rate at which it can chemically produce current. If it didn't happen prior its probably just the battery showing its age or possibly it wasn't completely charged. I don't think its anything to be alarmed about.

Maybe use a marine battery to run your trolling motor. Your standard car batteries don't have a whole heck of alot of capacity and are mainly built to produce enough high current for short durations to start your engine.

Thank you for the info. The house battery is a group 29 deep cycle. It’s one of the Walmart ever star batteries, dated 2015.

I just called minn Kota. They said the trolling motor should have its own dedicated battery. Right now my trolling motor runs off the house battery which also runs a modest radio, lights, pumps, etc. The other battery is the starting battery which only runs the engine. There is only two batteries in the boat. It is a small 16’ flats boat.

So should I (a) add a third battery and dedicate one to the trolling motor, (b) keep things as they are or (c) move some/all devices to the the starting battery and leave the second deep cycle all or mostly dedicated to the trolling motor? I am reluctant to add devices to the starting battery for obvious reasons.

The GPS uses almost no battery, you can run it off your starter battery, or even a small 12v UPS battery and it will be fine. The voltage of the trolling motor battery dropping under load is pretty normal...


Eta: is the everstart g29 a marine deep cycle?

Yes, it is a group 29 marine battery. Maybe I should just change it to run off the starting battery... I could also slide a small battery (like the one pictured) into one of the existing battery box.