How to estimate laptop sleeping time on battery?

"There's no way of telling, really. It depends on the laptop, the battery and the thermal conditions. I put a MacBook to sleep for well over a day with minimal impact on battery life, but that does not mean the same thing will happen on a different laptop.

Taking a stopwatch and measuring the impact on battery charge might be the only way, unfortunately :)."

"You don't have to run it all the way down to find out, though. If you wake it from standby to find 10% gone, then you can estimate it would last 10 times that particular sleep time. Still requires the stopwatch, though.

Another hint about sleep efficiency is to see it gets completely cold, or if there are any warm spots. Warm spots equals real power being used."