Connecting two 12v batteries for longer run time?

I’ve got a 12v bow mount motor on my new boat. How do I connect two 12v deep cycle batteries together to gain more run time than if I was just running them off of one battery?

Also, if one battery is weaker than the other, will it ruin the good battery? Thanks!

I am not sure how to connect them but if you are going to do that your going to want to get two new batteries that match or one will cause harm to the other.

Positive to positive and neg to neg ,both batteries should be should be of the same shape and size for best results

Make a pair of 8 gauge (or larger) jumpers, and connect the negative to negative, positive to positive. This is called a parallel connection, as opposed to the series connection if you want to create 24 volts from (2) 12 volt batteries. And yes, a weaker battery will draw a stronger one down.
HRG

the biggest problem is when you charge 2 dissimilar batteries one will over charge or 1 will under charge because both batteries won’t take a different charge when hooked together.

You will want to create the parrallel connection mentioned above. I would also suggest charging them seperately, meaning disconnecting them during charging.

Part of the problem, like Kooty explains, is that the batteries should be “seperated” from each other when charging. Take a look at this mini battery selector switch. If you hooked-up your TM positive lead and your positive charger lead to the common post, than run leads from the switch to each battery, you could then charge each battery (1 at a time), yet set the switch to “both 1+2” for the longer run time you’re looking for.
HRG
http://bluesea.com/category/1/products/6007

Isn’t pos to pos 24v parallel? Did the poster say 12v? Wouldn’t that be pos to neg? No expert here, just checking.

Positive to positive (and negative to negative) is 12volts. Positive to negative (series connection) is 24volt.

Thanks HRG! Now I know. I haven’t blown anything up yet. Did I say yet?

If you spend the money on that switch, I’d set it up to run off one battery. Then when that one runs down, flip the switch to the fresh one. Charge up the same way.

Also, if you do run the batts in parrelle, run you leads off ONE battery.

-J.

Battery size is not important if you use one bigger one smaller the smaller will charge faster yes but once its charged the bigger battery will continue to charge and the smaller will not also a battery tender will help prevent over charging both batteries the only reason i know this is. A im a mechanic and B ive ran several dual battery setups on my race trucks. But to each his own.

Ajs

Also as jon jordan said connecting both leads to one battery is the easiest. Heres a diagram of the proper wiring.And i forgot to mention if one battery is bad it will drain the good battery you can charge them and bring them to a shop or auto parts store and get them tested to see if they are good.

Did both my posts get deleted??????????

I still see them, but the diagram you posted is gone.

I had to do the same thing when I got my new boat…everything posted here is right on the money.

I think my computer is having a bad hair day but here,s the diagram again.

when you have a 24v system, (trolling motor) can you still connect a 12v locator to ONE of the battery’s, with out blowing the thing up? the reason for the question is my 520c is connected to the fuse panel under the dash with the power coming from the starting battery, to much interferace when i.m running the boat motor. how else can i get away from the interferace, and connect to what. Also when going across the lake at higher speeds i lose the depth reading and it just starts flashing wrong depths, what can correct this? my trans seems to be positioned right.

Locator should work fine as long as it hooked to only one battery and for the depth readings im pretty sure the locator cant keep up with your speed which is pretty common unless you have a high end locator.IM sure there is better terminology for this but im not up to date with it.

Thanks Andy, could i run an extra set of wires from the starting battery and connect directly to the locator without the interference problem will running the big motor? it’s an i/o merc. just thinking of all options and what makes sense with the less hassle but still getting? the BEST results?

jk

Try that it might fix your problem but im not sure i cant remember off the top of my head exactly what the problem is. One thing you can check is the plugs and wires on your i/o if they are not resistor wires and plugs it will cause interference when the motor is running. Mainly the wires would be at fault but the plugs may also cause this.

Ajs

Ok running batteries in parallel I get but how much difference in voltage is ok between batteries b4 one is weaker and causes the ‘good’ battery to drain.

assuming both batteries are charged and hooked up in parallel your trolling motor will draw from both at the same time.

I hope that helps a little.