Be careful when charging Odysseys via Genesis dual-battery kit

To maintain dual Odyssey batteries in a Genesis dual-battery kit, Genesis Offroad recommends, on their charging FAQ and YouTube video, simply to connect your charger to the Factory Positive and Factory Negative terminals.

For the purposes of battery desulfation, I would caution against doing this (see details below). Instead, I would recommend charging the batteries one at a time, and never in pairs. The YouTube video above suggests you can charge JUST the main or JUST the aux battery, by connecting the charger directly to JUST that battery's terminals. This is incorrect: As soon as the battery charger is turned on, you will hear, after 120 seconds, the solenoid "POP" as the Cole-Hersee FlexMod 48540 has bridge the two batteries together in parallel, and you are now charging both batteries in parallel, regardless of whether you have connected the charger to just the main or just the aux battery.

My recommendation: Disconnect the FlexMod Harness (that's the gray plug with 8 wires coming out of it) from the blue Cole-Hersee Smart Battery Isolator. This will prevent the bridging of the batteries via the solenoid. Then hook your charger to the main battery and charge it overnight. Then hook your charger to the aux battery and charge it overnight. Then plug the FlexMod Harness back in and you're good to go.

The following are details of why following Genesis's recommendations above can yield poor results:

The manual for my BatteryMinder 128CEC-1, which is on Odyssey's list of approved 12V chargers, issues a multiple very stern warnings against maintaining two batteries simultaneously (see below); specifically: "Never connect two or more batteries together unless they are fully charged ... only healthy, fully desulfated batteries should ever be maintained in sets of 2 or more ... attempting to desulfate more than one battery at a time will yield very poor results, as the strongest (healthiest) and not the weakest (most sulfated) battery will receive the majority of the desulfation pulse energy" (emphasis mine).