[Mr LeRoy]

As you suggest, checking the battery would be a good first step. If the battery is fine, then your only real option is to have a dealer reprogram it. If your Renegade is still under warranty I would expect (in fact I'd insist, if the dealer is reluctant) that it would be done as a warranty issue. You'll need to have both keys on hand when this is done so that both are coordinated with the vehicle.

 

[Mr LeRoy]

Don't give up until you've replaced the battery in the spare key. The simplest course of action is often the most fruitful.