I've bought the SIDO battery and charger from ebay a while ago for the 770. Mainly as fallback when I don't opportunity to charge the BP-5L.

The SIDO battery works fine in the 770 although it's empty faster than the official BP-5L. I think about 2 hours with full load.

The SIDO battery charges fine both within the 770 and in the charger. I haven't tested the BP-5L with the SIDO charger though.