I am using H-Energy 4000 hardcase. You are right, it is hard to put the pack into battery space, but I believe you can because I did it. You can't just release the battery tray, you need to take off the block which holds the back end of battery tray (small block a bit ahead the motor mounting space). Now you can slide the pack in and try to keep it as close to the top deck as possible, and then put the block back on while holding battery pack, and then the battery tray. its a bit tedious but this is the way I found I can put the lipo pack in. I also found if I also release the top deck, this work would be a bit easier. I checked the H-Energy website, the dimension for hardcase lipo packs are similar, only 1~2 mm difference in height and length. When my pack in the car, I can still move the pack for few mm, so I think even you use other packs, you should be fine. I hope it helps By the way, you also need to trim some parts (shown in the manual) and the most importantly, you need to trim the corner of the battery pack where close to the belt tensioner brace (you will know when you slide the pack in)