I have a pair of SMC HCL 5200 and a pair of gens ace redline 2.0 6300 lipoHV. Not unsurprisingly the gens ace are much better. One of the smc has a failing cell and it might have been used 6 times. I have to give it a few seconds on a nicad charge to bounce it back so it can charge normally, I should get rid of it. The gens ace has bullet connectors and cost way more and you need a lipohv charger to make the most out it, and that is also harder on the battery. The SMC batteries are about 1/4 to 1/3 taller.
I looked up the xr8 manual and slow red light is low voltage cut. You might have yours set high, your batteries might be failing, you might not be charging to 4.2v, or your expectations are more then your batteries capacity can match. I think a poor solder or sub par battery connector could influence things, but not sure.
If you want more run time you can disable boost or turbo and increase the throttle pwm. That will suck some of the fun out of it. I notice mine has less pep to its step before my low voltage cuts the fun and if you don't I would measure the individual cell voltages after a run to see if one is lower vs the others. Battery voltage sags under load so if one cell is .2v low on a meter, it might be 1.0v under load tripping the cut. Next time running it, let the lvc trip, unplug it and let the battery cool down, then plug it back in and try it, if you get more then a minute I would say its a failing cell. Then meter each cell anyways.
