How to avoid charging?
Barring some black swan type event where someone discovers super low power computing, super rapid charge batteries that last more than 2 charges or high capacity batteries then it is going to need power to do its job really (if they could have made them remote playback they would have. Some might try robbing power from the wearer (heat, movement, chemical being the main options, and movement is about the only viable one and its limitations are considerable*). Some might get the wearer to have clothes with batteries in them and some kind of inductive charger in that (or even just run the wires along your sleeves). It is not impossible some external chemicals are used but nobody is likely to want mini fuel cells on them really (certainly not radioactive generation and even less likely to be burning aluminium as that is also quite expensive and wasteful).
*though if combined with the clothes of later in the bit then that could do more. Would also be able to be sold as a weight loss aid; computer detects you need more power or have not burned enough calories and all of a sudden it is harder to raise your arm and that resistance being overcome is converted to electricity. Could do it now with motors but I would probably look to some kind of piezoelectric or similar carbon fibre you can change the mechanical properties of it with some small amount of electricity.
But anyway enough of going future tech predictions boy. I generally see smart watches as a solution in search of a problem. Have done since they were game watches (I had Mario), calculator watches, TV remote watches (though the prank options for those made them hilarious) and GPS watches (though they were at least nominally hardened to sweat and nastiness where phones might suffer more if you go swimming or get hot and sweaty. I certainly can't rule out someone finding a use case for a smart watch (notifications/basic reading without pulling phone out of pocket/bag, especially if you have multiple phones/tablets, being the main one that also makes sense to me. If you can tie it to something fun on bluetooth (all sorts of fun sensors there -- blood monitors, I saw a bluetooth machinists indicator the other day, cars have fun things for them...) then that too.) but I am expecting them to be niche and then either be a fashion accessory like normal watches are mostly today, some kind of hipster/technophobe thing when retinal/neural implants get to be good enough.