Air carrier First Officer reported the APU Fire Warning activated in cruise flight and the APU Fire Bottle low pressure light was on; indicating the bottle had activated. A divert was executed and accomplished where it was determined there had not been a fire.

Narrative

While enroute from ZZZ1 to ZZZ2 at FL240; we received a Master Warning and Check Fire Detection indication of an APU Fire. After looking over the checklist; we noticed the APU panel had the 'BTL LOW' light illuminated; suggesting the system automatically blew the fire protection bottle. We didn't know the extent of the situation so we decided to treat it as priority and divert. We were about 40 miles east of ZZZ3 at the time; so we declared priority; called for the trucks; and began our diversion. The Captain made his required calls while I flew the plane and loaded the box. Upon landing; the fire trucks checked out the plane and determined there was no indication of fire. We proceeded with a normal taxi to the gate and deplaned. After Maintenance completed their inspections; they found no evidence to suggest there was a real fire. As far as I know; we did everything we could to address the situation. The checklist didn't apply very accurately to the situation since we don't run the APU in flight; but still ran through it as well as we could. We didn't have any exceedances and we were below our max landing weight.I'd say the biggest lesson I learned is that sometimes strange things can occur that you can't really train for. In this case; the checklist wasn't much help because the APU wasn't running. In a situation like this; we needed to use the information we had to get the plane on the ground as safely and efficiently as we could. It was also a reminder to be aware of the best diversion options while en route. The Captain knew exactly where we should go which allowed for a safe and immediate diversion. In the future; I plan to think more intentionally as to where the best diversion location would be.