Hooking up two batteries with an onboard charger

[Capt Rod]

Ok I currently have a crank battery and one trolling battery. I want to hook up two trolling batteries. I have a 12 volt 54 lb motor guide trolling motor that last a half of a day. It looks like if I connected the two batteries positive to positive and negative to negative it will work, but will my onboard charger charge both batteries? I do not have the charger name or model because I am at work right now, but I can get that if it is needed.

 

[vipzach]

Re: Hooking up two batteries with an onboard charger

Yes, you can hook them up positive to positive and negative to negative. Your onboard charger will charge both batteries. You are talking about the two hooked together right?

 

[Capt Rod]

Re: Hooking up two batteries with an onboard charger

Yes I am talking about two batteries hooked together with battery cables. Thanks for the info.

 

[chuckz]

Re: Hooking up two batteries with an onboard charger

Just be aware that if you hook both batteries together without isolation, if one goes bad they both go bad.<br /><br />While charging the "deader" battery will charge first and the charging time will be doubled.<br /><br />Hooking two batteries together is cheap and dirty. It will work but may cause problems down the road. If you search for two battery discussions you'll find information on isolators and dual battery chargers.

 

[Capt Rod]

Re: Hooking up two batteries with an onboard charger

What kind of problems could it cause down the road other than the loss of both batteries? I have searched the forum while at work, and I am going to start reading again, but with an isolator in place where would you connect the trolling motor? If I connect it to one of the batteries then it would not see the other would it?

 

[Dunaruna]

Re: Hooking up two batteries with an onboard charger

A 12volt trolling motor draws high amps - it's basically a starter motor . Ideally you need a big deepcycle isolated from the #1 batt.<br /><br />What you are talking about doing will work better than just having one batt but both batteries will die sooner than normal, they will try and equalise, the weakest of the two will drag down the good one.<br /><br />It won't cause any other problems apart from the fact that you may be stuck without a charged starting battery.<br /><br />Aldo

 

[Capt Rod]

Re: Hooking up two batteries with an onboard charger

Let me make sure we are on the same page. I have a starting battery and it is not connected to the trolling battery other than the onboard charger, but with my charger the batteries are separate. My trolling battery will last a half of day, so I am going to hook another battery up to the trolling battery making it 3 batteries total. I would just go buy two new identical batteries to do this. However, if there is a better way to do this I am open to that too. I am new to this so any advice is welcome.

 

[Dunaruna]

Re: Hooking up two batteries with an onboard charger

I misread your first post, sorry.<br /><br />Will the two new batts be isolated from your main batt?<br /><br />You'll need deepcycles. Your plan is sound as long as your charger is 'smart'.<br /><br />Connecting two 12v batteries in parallel is effectively making one 12v battery but double the AH rating, if one dies it will drag down the other so testing them regularly and replacing them as a pair is recommended.<br /><br />Aldo

 

[Capt Rod]

Re: Hooking up two batteries with an onboard charger

Yes they will be isolated from the main. Thanks for the advice.

 

[cuzner]

Re: Hooking up two batteries with an onboard charger

Hey Rod, I think most people where assuming you have a switch... the benefits are you can charge either bank from the motor, and if your starting bat. is dead you can switch to your other bank to start your engine.Yes your charger can charge a 2 bat. bank. If you can you should match your trolling motor bank batteries, same size,amp etc.If you don't you will only be able to charge up the capacity of the weakest (in theory after you unplug charger, the 2 batteries will equalize). This stuff gets confusing.Anyway good luck.<br /><br /> Jim