Take the kWh capacity of the battery (5, 10, 15 or 20) and divide by the output of the inverter you choose (3.68 or 5kW). i.e. A 10kWh battery will take 2 hours to charge if you have the 5kW inverter.
These times are based on the battery being charged at the maximum power output of the inverter. The libbi battery may take longer to charge if it is being charged from PV panels only.