Not familiar with your charger

Some will only charge up to storage voltage from empty

Some will only discharge down to storage voltage

Some will either charge or discharge depending on the starting voltage of the pack

If charging up use your normal charge rate

If discharging you will more than likely be limited by the discharge power of your charger, regardless of what rate you enter

Most have very small discharge current rate limits (5 - 30 watts)

Check the spec sheets for your charger and it will tell you what the discharge limit is

Simply divide it by the pack voltage and you will work out the max discharge current

Example
20 watt discharge limit
3s pack

20w / 12.6v = 1.58 amps max discharge current

Cheers