I charge my RG350P overnight occasionally, and I've never had any issues. I always have it completely turned off when I charge it. It does stop charging on its own once it's fully charged, too.
One thing I would recommend is to try to avoid letting the battery FULLY drain. I let it completely die once, and the device was acting a little weird until I charged it up and hit the reset button on the bottom, then everything was completely back to normal.
I use this charger and this USB cable to charge it. I even bought a cheap little USB voltage tester because I read all those horror stories about people frying their devices, too. lol
It charges at about 5V/0.9A (which is totally safe for my RG350P) and takes about 4-4.5 hours to charge from 0-100%.
Stuff I'm using...
These two controller charging stands designed by /u/BearCubTeacher
https://www.thingiverse.com/thing:3744655
https://www.thingiverse.com/thing:3751848
Both available printed from /u/Zenyth3D:
https://www.etsy.com/listing/744857671/magnetic-charging-stand-for-valve-index
https://www.etsy.com/listing/707556478/valve-index-magnetic-charging-stand-slim
These are best used with cables with magnetic attachment recommended by /u/BearCubTeacher:
https://www.amazon.com/gp/product/B07HBZ3ZH9/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1
Dual USB charging adapter for the controllers:
Base station wall mounts (more compact and less visible than those that come with the Index):
https://www.amazon.com/gp/product/B00R96X9DS
Base station power cable extensions:
https://www.amazon.com/gp/product/B07QXKHHV8/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1