You shouldn't charge the battery to more than about 95%, just in case. (It depends on the battery and the charging circuit in the particular phone, but some batteries will lose a bit of electrolyte every time you get up to 100% (which doesn't actually happen until about 5-30 minutes (again, depending on the phone) after the indicator reaches 100%. (Which is why some people complain that as soon as they disconnect the charger, the battery drops from 100% to 99%.)
As far as the heat, that's normal. No conversion process is 100% efficient, including converting electrical energy to chemical energy (which is what charging is), and conversion inefficiency means heat. And the battery will stay warm for a while - it takes time to cool off back to room temperature. Leaving the charger plugged in, though,
shouldn't (it says in theory) cause any heating - the charging circuit in the phone should turn charging off when the battery is fully charged. (But if the phone is on, as soon as the charge drops a bit, the battery gets charged a bit. That's normal. If you want to see what's happening, install
CPU-Z and look at the battery tab (swipe left). I haven't had my phone on a charger since yesterday, the screen is almost always off, and my battery is at 82.4°F.
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