cranking battery question

-all electronics are wired to this battery (main motor, kicker, 2 hds 3s, all plumbing, radio, nav lights, etc.)
-I have a 150 mercury xl
-Battery is only 14 months old, connected to minn kota onboard charger, always plugged in when not in use.
-battery is interstate cranking group 29M, 800 CC, and 180 RC.

Lately I’ve been having a low voltage issue when trying to start the big motor later in the day. Motor will crank hard, lowrances will temporarily power down and then come back. My motor has always started, but sometimes I didn’t think it would.

I’ve been experimenting with how much power I’m drawing from the battery. Lately I’ve only been running one lowrance, livewell pumps on and off, and radio only sometimes. It seems as if its getting worse. Last night I was only out for 2 hours, longest I fished one spot was 45 min before running 1-2 miles to the next spot, only had one locator on and it happened at the end of the night after only being out 2 hours.

I’m taking the battery in to be load tested today, but does anyone have any other information that could help me diagnosing the problem.

Nothing to help, but sounds like a familiar problem I and others have had. Usually, and in my case, it was a bad battery. Took mine to three places, two said it was fine, one said it had a bad cell (?). Replaced it, and everything was fine. Sucks though.

Not sure what the live well pulls, I pretty much quit using mine and do the cooler thing now. I was a panfishing guy, and could go all day without running the big motor…

Navigation lights unless LED style will pull quite a bit. A one or two mile run would hardly replace the amps needed to start the engine, let alone the draw down between runs. I suspect a new battery will be required.
Early battery failure can be caused by too deep of a draw down between being fully charged again. You may want to investigate using a dual purpose battery for your starting needs. Also look to see about upgrading to LED navigation lights if not LED already.

I use a deep cycle battery for my main battery… starting big motor, kicker motor, multiple live wells, multiple locators, running lights, I’ve never had a problem.

I’ll never put a plain starting battery back in any boat I own.

Joe, its interesting you say that. The good people at interstate mentioned that as an option due to the fact the battery is being used so much for running electronics/accessories and they have plenty of power for cranking. But my battery was bad, cranked good the first time they tested and then voltage went way down the subsequent test. So I replaced with the identical battery as it worked very well up until recently and my boat dealership recommended doing that.

2x. I always use an deep cycle AGM batt for my starting/everything else battery. My starting AGM has 1100 marine cranking amps and can handle a continuous draw without draining the battery down in short order. Never had an issue since I converted away from a starting style batt.

I experienced a dead battery at the ramp yesterday morning. This one only made it 14 months and the last one made it 10 months. I will be looking for a deep cycle with enough CCA this time around. I originally had a deep cycle for my starting battery but it was short on CCA when it was close to freezing. Merc recommends 800cca for my motor.

I had a similar issue. With all the electronics powered up, check your voltage at the fuse block under the dash compared to the voltage at the battery. I had a 1 volt drop between the two.

My issue was too much draw on the fuse block for the size of wire installed. I am running an HDS8 and HDS5 on the dash, plus add a stereo, phone charger, smart gauges, powered NMEA links, live wells, etc and it adds up. My solution was to add a second fuse block with another run of positive and negative wires. Then split the load under the dash between the two blocks.

I left the pre-wired boat stuff as is. For my electronics and anything else I added I put in my own fuse panel. I ran 10ga to the panel and 14ga to any device or outlet. My starting batt is a group 31 AGM. My electronics don’t even flicker when I start up the F250. Also make sure the outboard cables are the first thing you place on the battery post. When you have multiple wires on the post always start with the heavest load terminals and work your way to the lightest load being last. That would make the battery charger connection the last one on the post. It does make a difference.