2009 Toyota Avalon Owners Manual - Page 357

4-3. Do-it-yourself maintenance n Before recharging When recharging, the battery produces hydrogen gas which is flammable and explosive. Therefore, before recharging: l If recharging with the battery installed on the vehicle, be sure to disconnect the ground cable. l Make sure the power switch on the charger is off when connecting and disconnecting the charger cables to the battery. 4 Maintenance and care 333