I recently built an electric skateboard and it gets pretty low mileage per charge, so I built a battery to replace the original one. This battery has 3x the current (6000 mah) and the same voltage at 25.5. The way I constructed the battery is by wiring 2 pack containers of 3.7v cell batteries together in series. Each of the packs use quite thin wires but the packs were designed to be used for this battery (but not necessarily in series). When I run the skateboard on its own it works well, but once I apply weight and strain, the motor briefly starts working and then shuts off, and the battery indicator says the battery is dead. Once I get off the board and run it without load it works again and the battery indicator shows full again? I have no idea why this is happening so any thoughts would be much appreciated, thanks.