Is it this from the Handbook? Jonathan Battery charging
Batteries generate explosive gases, contain corrosive acid and produce levels of electric current sufficient to cause serious injury. Whilst charging, always heed the following precautions:
• Before charging, disconnect and remove the battery from the vehicle – charging the battery with the cables connected may damage the vehicle’s electrical system.
• Make sure the battery charger leads are securely clamped to the battery terminals BEFORE switching on the battery charger. Do not move the leads once the charger is switched on.
• Whilst charging, shield your eyes or avoid leaning over the battery and keep the area around the top of the battery well ventilated.
• Do not allow naked lights near the battery (batteries generate flammable hydrogen during and after charging).
• When charging is finished, switch off the battery charger BEFORE disconnecting the leads from the battery terminals.
• After charging, leave the battery for an hour BEFORE reconnection to the vehicle – this will allow time for explosives gases to disperse, thereby minimising the risk of fire or explosion.