I have two batteries in my boat, one of which is primarily used as a starting batt and one is for the trolling motor. The batteries are the combination start deepcycle type and I have them connected in parallel with a batt switch. I am wondering if I can charge them both efficiently with the switch in the both position and the charger on one battery or should they be charged seperately. Also should a combo batt be charged on the deep cycle setting or the setting for a starter batt?

 

Charge them separately as they will have different charges needs. You don't want to cook one while the other is still charging. Shouldn't take very long to get them up to full, just make sure they have enough water. I always trickle charge my RV batteries, always.

 

12v batteries are used in parallel all the time in RV and Marine applications. If they are both RV/Marine batteries, they can be charged together. In fact, in two of my boats and all of my rvs, the coach batteries were in parallel - - it was impossible to charge them any other way. In most rvs, they parallel charge the engine battery (high amp type battery) right along with the RV/Marine ones off the alternator. Not the best way to do it, but gets the job done to a point.
Bob

 

Thanks gentlemen, I appreciate the info.

 

I have seen charger setups for exactly what you are describing...Dual Pro Xtra II

grantx5 is right...starting and trolling batteries have VERY different charging needs. While you may or may not damage one or both while in paralell, I would not charge tehm this way. One could wind up over charged and the other undercharged.

HTH

Tony

 

I have two identical batteries in my boat. When the engine is running, both batteries are switched on but when not being charged and I'm just running the depth finder or radar, I always switch to only one battery. I always want a fully charged battery in reserve to start the engine. Also, I don't want a weak battery sucking both of them down so that's another reason not to keep them switched on. This has been my practice for both and sail & power boats.

 

As an aside, FYI that in dual battery setups, make sure you have two of the same batteries (size, manufacturer, etc), and if you have a bad one, change them both. They are like "twins" and need to be considered a "set", or problems may develop down the road. I have a lot of military vehicles with dual battery setups, and that advice, shared with me years ago, has served me well.