Handling tips on Airsoft NiMH and Lipo batteries (extracted from ASG website)

For NiMH Airsoft Batteries:
- Recharge your battery immediately prior to use
- Full discharge is not necessary – NiMH as no memory effect
– In no situation your NiMH temp. should exceed 40 degree C
- NEVER charge you NiMH with a LiPo charger or vice versa
- Store your batteries in a cool place (not freezer) and at approx. 40% charge
- Safe maximum charging current is 1C (e.g. 1000mA battery should be 
charged with max 1000mA) or never exceed 2C
- ALLWAYS disconnect battery from charger when charger is turned off

For Lipo Airsoft Batteries:
- NEVER fully discharge you LiPo
- When your LiPo is completely depleted then charge it immediately
- In no situation your LiPo temp. should exceed 40 degree C
- NEVER charge you LiPo with NiMH charger or vice versa
- Store your batteries in a cool place (not freezer) and at approx. 40% charge
- NEVER exceed maximum ‘C’ load even for short periods (e.g. Max load of a 
1200mA 20C battery = 24000mA = 24A)
- Safe maximum charging current is 1C (e.g. 1000mA battery should be 
charged with max 1000mA) and NEVER exceed 2C
- ALLWAYS disconnect battery from charger when charger is turned off
- Remember a electronic switch system draws a small current when idle – so 
protect you battery and disconnect it from the gun immediately after use

Below are extracted from RC Group Forum for Lipo batteries too:

•Use only a charger approved for lithium batteries.
•Make certain that the correct cell count is set on your charger.
•NEVER charge the batteries unattended. 
•Use a safe surface to charge your batteries 
•DO NOT puncture the cell, ever.
•If you crash with your lithium cells they may be damaged
•Charge your batteries in a open ventilated area.
•Keep a bucket of sand nearby