Originally Posted by
Jonestrollingmotor
Either way will charge the battery, with neither being incorrect. I've always put the positive on one, negative on the other -- but that's because it just looks neater to me. In working with starters and alternators, you'll find 18wheelers which require a lot of amperage to turn the starter connected to the same battery, the two more in parallel with that battery (positive to positive to positive and negative to negative to negative). The alternator charges is great and the starter all works great. The same principle applies here. However, with that in mind, be aware that a bad battery in the system becomes a load and will draw power trying to equalize from the other batteries in the parallel system. A more efficient way in a two battery system is use a battery selector switch. This isolates the batteries, when one runs low, simply turn to the other battery and you have a full battery again to work with. When charging, change to both and the charger will charge each battery in parallel.
John