I remember seeing a HDP2 battery "mod" that involved cutting (2) wood dowels the same diameter and length of (2) AA batteries, and wiring them up to accept a 12vDC battery. Basically, these wood dowels fit into the first two slots of the standard battery box in the P2 and allowed the user to use the battery meter on the P2 to gauge their external. However, this required you cut a slit in the battery cover to allow the wire to go through... I always wanted to do this, but I ended up using many rechargeable AA batteries in the standard battery slot when ever I taped... It helped that the venue I taped most of the time gave us AC power, so I used the wall-wart...
Terry