Charging two 12-volt batteries in series…

How-To Charge a Mobility Scooter 24-Volt Battery Bank with Battery Tenders

Hey Mike,

I have a mobility cart that works off of two 12v batteries in series for 24 volts. I have two small BatteryTenders ordered to keep the batteries charged/maintained or at float voltage. I plan to hook a charger to each battery. One twelve volt battery one twelve volt charger. My 24 volt charger does not have maintenance charge feature and cuts off when the batteries are charged. 

Is it necessary to disconnect the connection between the positive of the first battery and negative of the second battery when the two BatteryTenders are hooked up? The 24 volt charger will be disconnected and the cart switch off. 

I have enjoyed your writings for years. Learned a lot.

Thanks - Aubrey

Dear Aubrey,

Great question! You don’t have to disconnect the wiring to charge a pair of 12-volt batteries in series for a 24-volt mobility scooter. In fact, Battery Tender makes a 2-Bank charger/maintainer for the marine industry that works exactly as you describe.

How to connect chargers for two 12-volt batteries in series

According to Battery Tender Tech Support, their 2, 3 and 4-Bank chargers have isolated outputs, so you can use them to independently charge 2, 3 or 4 batteries in series without disconnecting anything. And since you already have a pair of single-bank Battery Tenders, you can hook them up the same way that’s shown in the diagram below.

More on this later

Since Battery Tender sent me both a 1-Bank and 4-Bank charger, I’ll do a few experiment/demonstrations with both units for several battery configurations. Please let me know if you have any more questions in the meantime.

Let’s play safe out there…. Mike