The battery holder is a skimpy piece of metal located on the topside of the folded bottom edge on the right side panel. Basically you have to lay down on the floor to find it. The side folds over parallel to the floor on the bottom and the holder is screwed to the top of that bottom folded edge.
I had the same experience and then I discovered the burners on top only get a spark when I push in the knob for the oven. Pushing the knob for the burner allows the gas to flow to generate enough heat to allow continued gas flow. So push in the oven knob and see if both burners get a spark.fiddling with the battery for that darn thing. Replaced it with a couple of known good batteries, and it still didn't work.
So we just use a BBQ "clicker". Less heartburn.
Good luck!