ok for battery if the device is plugged into ac charger most of the time?
With the arrival of so many fixed batteries---in phones, my laptop and my tablet---often I find myself on AC even after the battery is fully charged. I used to use my old laptop with no battery. But that's not an option any more.
Battery tech has improved. I remember many old debates and conventional wisdom that using the device all the time with battery in and plugged in as well was bad for the battery. Is that still true? Lith ion polymer.
Re: ok for battery if the device is plugged into ac charger most of the time?
Not anymore unless you have a really old battery pack or a shady 3rd party one. Good battery packs and at least the ones from major manufacturers have protection circuitry that will actually protect them from overheating and overcharging if you keep them plugged in.
However, it is a good idea to let the batteries work on their own once in a while. While the memory effect is long gone, new battery tech does like to be used, so if you want to extend the life of your battery, you have to let it complete a few cycles every now and then. It's good for battery gauge calibration, too.
But there's always the chance you get a bad unit and that either the charging circuit is faulty or you have a bad battery pack. In that case, well, it was going to fail anyway.