Nikon Coolpix S51

Hoping someone can shed some light on the advisability of a 3rd party battery & charger vs the mfr's genuine equipment. I read several queries in the Nikon Coolpix forum but with inconclusive (my opinion) results. My Coolpix P520 came with a single battery. The Nikon-supplied charging scheme allows only in-camera charging. I also have a pocket Nikon (S51) that has an external charger. While the batteries appear similar the P520 is too large (esp length) to fit the S51 charger. 1. Is there a...