cool bike. i have a DH bike set up too. i really like your dropout mod, very outside the box, i never would have thought to pinch the axle.. anyways. About your battery situation. for a while i ran turnergy multi star 6s 16000mah in series and they worked wonderfully I still have them to this day and they still balance they did not puffs and I've had them for almost 3 years however I do not run them on my downhill set up anymore because I was afraid of a fire because I wrecked a few times and one time the battery pack ripped off of my bike and was hanging on by the power cord luckily that did not break so now I use a hard case 18650 cell battery pack with metal hose clamps reinforcing it to the frame and I have not had a problem as far as strength goes and I find it's much more durable then having a lipo setup on an open frame like that. i use the lipos on my commuter bike and I can charge them on my Turnigy reaktor charger and power supply pretty quickly individually and I can also charge them on a parallel board but you can only put so many amps to that parallel bord. Individually they take about an hour and a half to 2 hours a piece at 6 amp charge. Which is much simpler than the schematic you're showing which is very possible but man that's a lot. and taking wires on and off and you'd be better off using a BMS to control your lipo charge in a situation like that. check out em3ev they make awesome batteries and the price is actually pretty good. Also something worth noting for off-road use a Twist throttle grip can kind of be a pain in the ass my personal preference is the thumb throttle because I can still have a good hold on my bars when I'm shredding and I can control my throttle a lot easier like riding a quad. Good luck with your build I can't wait to see the finished product.
