Avoid excessive re-polling of batteries after line-power changes

Should be mostly obvious.

The "power-supply"/is_power_supply related change is not really needed. Seems sane, but need to double check it as it changes the behaviour slightly (i.e. "power-supply" becomes sticky and does not change anymore when you remove the battery. However, that seems reasonable, a missing battery can't supply the laptop, but the fact that is is missing is already known through "is-present".