Dead starting battery

[tnbassin]

I have a 2017 RT188 and had to jump off the Mercury 115 today after about 6 hours of fishing. It has everything hooked up to the starting battery except for the trolling motor. Doesn’t the motor charge the battery when running? I made a 9 mile run mid day. I would have thought that would have charged the battery. I guess I was wrong. I just hadn't thought about it until today when the motor would not turn over. I jumped it with the trolling motor battery. I crappie fished today with all 3 depth finders on and a 12v aerator for the minnow bucket. I also turned on and off the ligewell aerator throughout the day. Anyone else run in to this? Or do you always remember to turn off all your electronics off every tine you move and stop? Or do I have something wrong on my boat?

[CatFan]

Unlikely to keep it charged like that. Takes a big battery to run electronics and pumps all day.

[buzzzzbait88]

Not sure what size battery I had compared to yours, but when I had a skeeter I'd make a couple mine to my honeyhole and sometimes sit all day long with graphs and livewell running and not have any issues. Shoot just last year we won a tournament off 1 spot. Ran there at first light and sat all day with graphs and livewell running and still turned over fine at the end of the day. Granted we never had these new large screen electronics like the new ones and I'm sure those draw a significant amount of battery.

[Great Scott]

You could have some weak cells or even a dead cell.
If its not a sealed battery, you can ck the cells w/a
hydrometer. LDS

[Panama]

Boat motors don't do a very good job of charging the starting battery....

If you are running a lot of stuff....and you are....you need the biggest motor battery you can get. Or you need another battery for your accessories. Make sure and always take an emergency jumper battery. The new style small ones work great and are about the size of a can of beer and not expensive and will start a boat motor.

Also, you might have only a two bank charger for the trolling motor....that won't cut it for what you are doing.

[one-over-par]

That's a good reason to add an extra deep cycle battery just for electronics, pumps, and lights...
That way the starting battery is for just that, starting the motor only.

I run 2@27's for Trolling motor,
the starting battery just for big motor,
and an extra 27 size for all electronics.

All charged back at the house with 2@ 2 bank chargers,
one just for trolling batt's and the other charger for the other two.

This was all done because I also had to jump the motor off of trolling batteries one time... never again.

[slonezp]

Is your onboard charger connected to the starting battery or just the TM batteries?

[ncbass]

What size battery do you have? I run an Interstate 27M-XHD and have never had an issue, run three graphs and pumps all day and she starts quickly every time (Merc 115 Pro XS 4s), you got a problem somewhere...

[mysuzytoo]

I would say your big motor battery is done. You need an AGM battery if your 115 is an Optimax. The batteries most dealers put in new boats just aren't enough for the Optimax and the goodies. Look at recommended batteries in the Mercury forum here on BBC. Mine went south after two years, and I got a Group 27 X2Power from Batteries Plus and it did the trick for me and my 150 doing the same kind of stuff you're doing.

[richg99]

Of course, it is possible that your charging system fuse has blown. I'm not certain how to check it,....but....if you have a multimeter, I suppose you could just check the battery voltage when the engine is turned off, and then check it again with the engine running. It should show a higher voltage if the charging system is doing its job.

I agree with all of the comments about needing a big, fully charged, battery on these newer electronic equipped boats.

Incidentally, most auto places will come to the parking lot and check your battery, under load, free of charge. Sure beats hauling that heavy thing in to them.

[KP1923]

This is what I run in my 2015 RT188 with a Yamaha 115HP. Replaced the factory supplied starting battery after 3 years, which was a Continental brand I believe, with the one below. Boat came with a Dual Pro on-board charger, and I keep it plugged in when it is in the shed. Have not had 1 issue running electronics or TM all day long on Rayburn, Fork, or any other lake I fish regularly. YMMV......

https://www.batteriesplus.com/batter...7m/sli27agmdpm

[tnbassin]

Ok, now I am officially scared. Just got home and checked my Interstate cranking battery and it is 3/4 charged. Something else is going on. What scares me the most besides having to be without my boat for a while is that this could be one of those hard to find problems.

And yes, For someone that asked, I have a 3 bank charger.

[KP1923]

Sounds like a bad cell in the cranking battery....

[tnbassin]

Sounds like a bad cell in the cranking battery....

So it can be 3/4 charged and have a bad cell?

[njpaulc]

Change the leads on your battery charger to see if the battery will take a charge, if it doesn't, you need a new battery, if it does you need a new charger.

[billnorman1]

3/4 charged is an arbitrary figure. Hit the motor trim up and down fully and AFTER a minute check the battery voltage with a digital voltmeter. If it doesn't read at least 12.4 volts DC it is either shot or not being charged. Then, plug in the charger and the battery volts should read at least 13 volts and climbing. If not, your charger is probably defective.

[KP1923]

3/4 charged is an arbitrary figure. Hit the motor trim up and down fully and AFTER a minute check the battery voltage with a digital voltmeter. If it doesn't read at least 12.4 volts DC it is either shot or not being charged. Then, plug in the charger and the battery volts should read at least 13 volts and climbing. If not, your charger is probably defective.

Sage advice.....Ken

[bunz559]

Last week I completely drained my cranking battery as well. It was a 27 Interstate cranking battery. Hot day so I had the livewell on manual for long durations at a time. We were crappy fishing so we were mainly anchored with minimal boating. When it was time to go, battery was just dead! I tried jumping it and it was a no go. Good thing I was on a small body of water and my trolling motor and batteries had just enough juice to get us to the dock.

[gdi]

At what RPM does the motor really start charging the battery? Also at an idle what would you see for an increase on a volt meter from not running to just starting the motor up?

[BoatBuggy]

Cranking batteries aren't meant to be drained the amount they are with today's electronics and other goodies. If you want to bring up the charge a battery while on the water, you'll need to do a good 30'ish minute run. Get yourself an AGM cranker and don't worry about it anymore. I have a Group 31 AGM cranker in my RT198p.