The APS CRS Battery Stock has been available for sometime now. PDW-style to match compact/SBR AEGs, it has a large space in the buffer tube to accommodate a stick-type Lipo Batter. It is lightweight and it is collapsible and cann for APS and other Marui-spec M4/M16 AEGs. Here is a video showing you how to install one on your AEG.