HPA Engines also work on a battery and these LiPo's are specially developed for HPA systems because they have very low MaH. A HPA Engine is so economical with power that the battery for this kind of systems does not need high MaH values compared to for example AEG systems.
Battery for HPA
Nano-Tech 7.4V 180MAH Lipo Battery for HPA
ASG 7.4V 250mah 20C lipo battery for HPA
The 7.4V 250mah 20C lipo battery for HPA by ASG
Balystik 7.4V 300MAH micro lipo battery (HPA)
The 7.4V 300MAH micro lipo battery (HPA) by Balystik