DIY 9V Rechargable Battery Replacement (850mAh @ 7.4V)

Since I was sick of buying low capacity 9V alkaline batteries, using shitty NiMH rechargeables, or buying overpriced LiIon ones, I ordered fitting LiPo cells and connectors from China.
The resulting battery has a nominal voltage of 7.4V, peaking at 8.4V when fully charged (s cells in series) resulting in a capacity of 850mAh. The lower voltage should not matter, since devices using 9V batteries usually run them down to below 5V and the cutoff for the LiPo cells is ~5.5V.

Since the packs are