Charging Batteries In Parallel

[B@ssCrzy]

So I am looking at upgrading my 12v trolling motor battery from a single to a double system with two batteries connected in parallel.  The problem is that I only have a 2 bank 10 amp on-board charger.  I don't get out every week and so sometimes the boat sits for a while.   So I want to make sure that I am keeping all the batteries hooked up to a charger.  Can I get away with hooking both the deep cycles up to one of the banks, and then the other to the starter battery?  Will 5 amps per battery be enough to charge them back up quickly after a day on the water, if I am going to fish again the next day?  Any thoughts would be helpful.  Thanks

[joefish]

Should work OK.

[MikeinFresno]

yes, it will work fine

[B@ssCrzy]

Cool.  Thanks fellas for the input!!

[WIGuide]

It might work better to hook you two bank up to both TM batteries, and buy a single bank onboard charger for your starting battery. 

[Way2slow]

Ahh, sorry Charlie! but your charger ain't gonna do what you wanna.

You stated you have a 10 amp two bank charger. That's only five amps per bank which ain't really big enough for one deep cycle battery.

Now, you throw two batteries, lets say they are 105 Amp hour, in parallel. Even if you only run them down to a 50% state of charge, that's 105 Amp hour you are going to have to put back in them. DO the math, for 5 amps to deliver 105 Amp hour of charge, even in my simple mind that's 21 hours it's going to take to recharge them. If they are down to 30% charger, you had better plan on just fishing twice a week.

Not only is it not going to charge them within any reasonable amount of time, it will eventually let the batteries stratify, which will ruin the batteries.

[B@ssCrzy]

Ahh, sorry Charlie! but your charger ain't gonna do what you wanna.

You stated you have a 10 amp two bank charger. That's only five amps per bank which ain't really big enough for one deep cycle battery.

Now, you throw two batteries, lets say they are 105 Amp hour, in parallel. Even if you only run them down to a 50% state of charge, that's 105 Amp hour you are going to have to put back in them. DO the math, for 5 amps to deliver 105 Amp hour of charge, even in my simple mind that's 21 hours it's going to take to recharge them. If they are down to 30% charger, you had better plan on just fishing twice a week.

Not only is it not going to charge them within any reasonable amount of time, it will eventually let the batteries stratify, which will ruin the batteries.

Hmmm....don't like the sound of that, but that makes sense.  May have to look into getting a single charger for my cranking battery and then using both banks for the trolling batteries.

[MDBowHunter]

I would ditch the 12s and get yourself two golf cart 6 volt batteries and hook them up in series. I guarantee that they will out last two 12s . I just switched over to 6volt golf cart batteries and they'll last all day on a single charge, actually I've run mine all day and have only been as low as 56% charge at the end of the day. Plus you can charge them both at the same time with a 12 volt charger. Another thing to watch when you hook up two batteries in parallel is it will double the amp output, and in the case of a short it could potentially catch fire and burn your boat up if the wire being used can't hold the combined amps. My boat is an all electric reservoir boat, I travel with two transom mounted 55# thrust that uses 4 6 volt batteries, and while fishing I'm running a bow mounted 55# thrust motor using two 6 volt batteries. Switching over to 6 volt batteries was the best change I've made to my boat...

[Bassin Bob]

I have the exact setup you described and it works great.  I hook both TM batteries to one bank and the starting battery to the other.  It doesn't take very long at all for a charge (4-6 hrs depending).  I just hook up after a day on the water and everything is ready to go in the morning.  Why not try it out before you buy something you may not need.  You will probably be very pleased.

[Ken l]

This will work. You don't say how big your batteries are but two 105's sounds at the upper end of what usually applies. Bringing them down to 50% would require a long day and a big boat. Could be.

Do yourself a favor and buy AGM's. The reason that 6 volt has merit is because they're AGM's.

[nicksmurf111]

Only parallel batteries if they are exactly the same and brand new.  If not, they will have a death match.  I'm not sure how many amps you need, but I'd be inclined to charge them at a moderate rate, then float charge them with 2 amps until you use them next.

 

I second the AGM's or golf cart batteries, both are great ideas.

[B@ssCrzy]

Golf cart batteries look like an option except for the cost.  A lot more expensive than regular deep cycle to get the AH that I need.  I had really good success with my wal-mart battery.  Got 6 years out of it so will probably just go with that.  Thanks for the input guys.  Appreciate it.