Batteries' "fully recharged in" time does not account for the 80% charging efficiency.
The charge time displayed in the terminal when a battery is selected does not account for the 0.8 efficiency multiplier. (Like the Jump Drive does)
A large-grid battery (3 MWh max, 30% initial charge, 12 MW input) displays a charging time of 10 minutes. The actual time with the 20% loss is 13 minutes.