Most tablet battery specs I have seen are in the 3-4 Amp hour (provide that amperage for 1 hour before voltage drops below usable rating - around 3-3.7 volts) range - they usually specify them as milli-Ampere hours so 3000-4000 mAh. (http://www.batteriesplus.com/t-faq2.aspx#10)

So at max charge with 3.7 volts times 4 amps, that would be 14.8 Watts - hardly anywhere near 1000 (1 kilo) watts (as I recall my basic electronics/physics classes...).

I believe the main danger of concern is from the potentially explosive chemical reaction to excess heat with Lithium-based batteries.