Glad you went with proper batt for field cahrging, that kills a car batt since they're not made internally to stand the deep discharges.

The old Duo may be hard to find - dealers haven't been able to re-stock due top the new SuperDuo thats about to be released. It will jump the charger power from 2 x 18watts to 2 x 300watts with 20amps charge rates for each port. If you need the charger output power, it'd be worth waiting for.