I just got an E-bike and I love it but now want More stuff to put on it.

I have a bell 20 function computer ( fancy cheap speedometer) a Bell head light, and a Bell tail light.

I was thinking about battery operated turn signals. Do they even make that?

What are some other cool battery operated gadgets that people put on bikes?

You may want to re-evaluate your head and tail light. As far as I know, Bell doesn't make ANY head or tail lights that are worth the firecracker it'd take to blow them up. If you plan to ride at night at all at any kind of speed, you're going to need better.

They make turn signals but I haven't seen any that aren't little junky plastic toys. And IMO it would be dangerous to rely on them anyway, they're too dim to be seen in the daylight (the ones I've seen anyway) so you still should use hand signals.

Are you looking for needed functionality, or are you just trying to bolt on anything cool for fun? If the latter, get a 12 volt tap off your battery and go to town with low-down-glow or whatever other pimp crap you can buy at Wal-Mart.