You hook up the charger to your standard 12v field power source!

Ok that sounds like a smart alec remark but it's not intended that way.

Most people who own electrics have a way of recharging the batteries at the field.

This can be something as simple as hooking the charger up to your car battery, or ( as in my case ) a dedicated charging field box with motorcycle batteries and multiple chargers and ports hooked into a self contained package.

If you wish to charge the batteries at home, you'll need a 12v DC output wall charger capable of at LEAST sustaining 1.5mA of output power.

Rat Shack has these and you may already have a suitable charger in box box of "unknown" wall warts.

Just make sure it is 12v DC positive tip 1.5A output ( higher than 1.5A or 1500mA is ok, less is NOT! )...