for the one that is sitting outside, I have a solar panel (1.8w and 103mA max) facing south... connected to the cigarette lighter. Rarely driven in the last year... it starts fine. For the indoor one, the battery is disconnected and trickle charged once a month with a trickle charger "Noco Genius G1100", (corrected model number), it is not a 1100 amp booster, only a trickle charger , rather fancy... because it reboosted the battery capacity, even after 2 months the battery is still at 12.6 volts.
Noco is made in the USA , since 1914...