well you risk going from a battery that lasts a 1/2 week to a battery that lasts 1/2 a day at best . other than that it's proabbly a good move
the KF slowness will probably be cured by a hard reset, [ google it] or as a last resort a factory reset.
you should expect to be charging any tablet overnight. amazon tablets lose ~10% charge nightly on standby even if unused