Someone had one on a lower Owyhee trip this spring. Brought a passel of batteries, and towards the end of the trip had lots of juice left. No recharging on water for her, and she stayed nice and toasty. To conserve batteries, she wore a coat over the vest to keep the heat in. That seems like a no-brainer. Towards the end of the trip, she skipped that because she had so many charged batteries left. I think it was a Milwaukee brand; their family has lots of tools/batteries, so the power wasn't an additional investment. Not sure how waterproof they are. There are now battery powered garments for SCUBA diving. I know they work under drysuits, and I think there are some that work with wetsuits so should work around water.
My name isn't actually Will.
I live in the Willamette Valley about a half mile from the Willamette River.