Battery charger info: https://www.revrobotics.com/rev-31-1299/
Charge rate
Minimum: 1.5A
Maximum: 3.0A
Recommended: 1.8A or 2.0A
Do not overcharge
Disconnect the battery from the charger once it indicates a full charge.
Typical charge time does not exceed 2 hours.
Do not charge a battery that hasn't been discharged significantly.
For example, running the robot under minimal load for a few minutes will not significantly discharge the battery.
Minimum no-load voltage: 9.0V
Discharging the battery past 9.0V can reduce the lifespan of the battery and can permanently damage the cells.
Periodic dips below 9.0V when under load is expected and OK.
For example, don't forget to unplug your battery after you are finished running the robot and don't run your robot until it completely stops responding!
Temperature
Let the battery cool before and after charging.
The battery may feel warm after heavy loading or after charging. This is normal.
https://ftckickoff.allendalerobotics.com/wp-content/uploads/2016/09/Care-and-Feeding-of-FTC-Batteries.pdf