For the Samsung Focus we were satisfied with generic batteries and chargers like this one:
These batteries are still working OK after a year of use although they only last about 80% as long as the name brand batteries and according to our kitchen scale weigh a few grams less. The charger just cut out and fails to charge after a solid year of daily use. I opened it up planning to diagnose with the multimeter, but never got around to fixing it. Really though for $13 it wasn't bad for 2 working spare batteries. So I'm looking for something similar for the 820.