This is my favorite of the multiple I own— https://www.amazon.com/CamelBak-2016-M-U-L-E-Hydration-Pack/dp/B01787QHWC. You can most likely find it cheaper outside on amazon, but it’s worth every penny in my opinion.

This is the Camelbak MULE there is a smaller zippered pocket at the very top separate from the water compartment. I hope to keep the battery packs in there. Last year I had a different hydration pack and just used a ziplock bag and duct tape to keep it water proof but still let me turn them on/off.