The plunger lift controller has a built in battery charger that uses the provided solar panel to recharge the battery. If for any reason, an approved battery does need to be charged (ie: loss of solar power source), ETC has built an inexpensive wall charger that falls within the battery parameters and has a preinstalled plug to fit the connector that is crimped onto the battery.
ALiEn2 Battery Charging Parameters
Voltage, Charge = 7.3 V
Current, Maximum = 375 mA