Thread: what size battery do I need ?

What outboard do you have?

2012 Merc 75 hp 2 stroke

I just changed over to a size 31 cranking battery. I run two birds, one console finder, two live wells, and front bait well and was getting low voltage readings as the day wore on causing me to constantly power one of the birds down. So far all is good. A buddy advised me to do this 2 years ago and now have to hear it from him. Just have to learn some things the hard way. Hope this input helps.

I'm running 2 birds ethernet ,live wells which use the same pump ,lights , dash FF on rare occasions , bilge which only gets used when I put the plug I the wrong hole lol also have 2 12 volt sockets ,I use the one up front to run engle bait cooler , last trip I just used the birds and live wells ran up past eagle creek from Coon then back fished a couple hrs at coon went start the motor click click click. , tried to jump with TM batteries but no luck

GoBob, I went from 24 to 27 deep cycle and so far all has been good but if you have room I would spend the extra few dollars and go for the 31.

Well, in general I'd advise a 29 or 31 (all but the same size), but before you throw money at it, you may want to confirm that your charging system on the boat and your charging at home aren't the source of the problem or contributing to it.

First, are you charging between trips? Does the charger indicate the battery reaches full charge? Ever let it sit for more than a month without charging it?

Assuming the answers to the above are yes, yes and no, have you ever checked the voltage on the battery when the engine is running more than 2000RPM? Should be about 13.5 to 14.5V, probably more toward the high side since you are having dead battery problems.

I have a onboard charger that charges then maintains like a trickle charger, no I haven't checked it while running, would need another adult I trust to drive it while I checked, yes I put it on the charger after my trip and at the camp ground , I checked it when I got home it had charged at the camp ground had 13 v checked it again today still 13 v . It's currently not on the charger. I put a 27 deep cycle in place of the 24 cranking battery, the cranking battery is on a floor mat in the garage still at 13 v. It is 4 yrs old

Add Volts to your overlay data and that will tell you if the motor is charging. Also you can connect the livewell to the TM batteries.