So you just run the + and - cables from the second battery directly to the terminals on the first battery?

I think we need to know where to put the + and - wires

 

To make it easy i bought 2 new batteries, both with top and side posts. I used the top posts on the battery in the original position as the main terminals that the truck hooks up to. I ran 4 gauge wires from the positive of the driver side battery to the positive of the pass side battery, negative to negative, using the side posts. That doubles your available amps, and reserve capacity but the truck remains 12V. If you were to go positive to negative you would double the volts creating a 24V system. DO NOT DO THIS!!!! you will fry everything.


You have to use 2 batteries of the same size, and roughly the same age. Otherwise if 1 battery is 10 years old, 1 battery is new, the 10 year old battery will discharge faster than the new battery and cause the new battery to lose its charge faster. The same goes with using 2 different sized batteries, 550 CCA vs 1000 CCA. They will also not accept a charge at the same rate.

I hope that makes sense?

 

Really it depends on what your goals are. Two starting batteries in parallel doesn't make as much sense to me since there is already plenty of cold cranking amps to turn over our gassers with one battery.

Of course two paralleled starting batteries is better than only one but fr my purposes there is an even better option.

I like a second battery to run accessories off of. In that case it makes a lot of sense IMO to run a deep cycle battery in an isolated/parallel configuration. It's parallel when the truck is on so the deep cycle gets charged with the normal bat, but when the engine is off you can run the deep cycle way down like 50% or so without killing your starting battery. Starting batteries discharged that deeply will die after only a few cycles whereas depp cycles are meant for it.

The way I set mine up the deep cycle adds to my camper battery capacity too. This allows the alternator to charge all four batteries when the truck is running and allow the camper to utilize the extra capacity when it;s shut off and I never have to worry about discharging my starting battery. Of course nw I probably need a 130A alternator so I wont fry the oem one after starting up the truck when all the deep cycles are way down on charge. Have to remember to run the genny for a while before starting the truck to save the alt I guess in the meantime. lol

 

I couldnt agree with you more. I decided to run 2 in parallel because i plow, with 1 battery i would notice my gauge go from 14+ volts down to 8 when using the plow.