When we action a stadby power check on the ground on a B757/B767 we select Standby power to BAT. The Battery and APU battery discharge lights come on after a few seconds. We leave it at BAT for a minute then select AUTO. We look on the Elec Maint page and watch that both batteries recharge. It takes over a minute for the batteries to come back to normal.
I hope that lessons have been learned here. When the QRH says 30 mins, it does mean land at once. Perhaps this should be emphasised for those that don't understand. As this crew found out there are loads of circuits connected to the Bat and Stdby busses that make life difficult when they fail.
With hindsight they would have been better off reselecting the Standby switch to Auto until they were within 30mins of landing.
The battery lasted longer than 30mins because a lot of the systems were still using main bus power as it was available. The 30 mins is when you only have battery power. Many systems have dual supplies, they will use AC Main bus power when available, and change to Stdby power when it is not.