Does anyone know where the battery backup is located in the 05 H2?Light is solid red and keeps saying "phone not available"

 

Just taking a guess from your low post count...if you just got the truck- It probably was never upgraded to the new onstar system when they phased out these older modules 3 years back.

It was analog cellular.

 

Im not sure but blu-tooth option just works tru on-start with limited minutes you need to buy with Verizon ... Anyway thats only what I found in a forum .
There is a module you can connect to get it work with you regular cell plan