Hi, I habitually allow my batteries (slate, laptop) to drain almost completely (to 8 or 7%) before connecting to power source. I usually don't connect to power source until the battery is that low, even if an AC source is available. On the other hand a friend uses external AC power exclusively, depending on battery only in the absence of an external power source. Is it ok to work with AC power even when the pc battery is fully charged without damaging the battery? Or must I drain the battery each time before connecting to external power source?