This fits the MP5A5 next generation model but the extended rails at the 3 o'clock and 9 o'clock positions will scuff up the side of the receiver a little bit. The only battery that will fit is the LIPO 20C one that is extremely flat and shorter than the AK style one. There won't be any wiggle room if you place the battery at 6 o'clock position of the rail, but it will easily fit the 3 o'clock and 9 o'clock positions and move around a bit. Wiring placement can be a little bit tricky and with too much force and bending, the plastic wrapping around the cables will expose the wiring.