I did the battery mod a few weeks ago to keep up with my wife on her ES4, thing is I'm not convinced. I've used the parallel wiring method, using a 36v 12.8ah battery pack and modded 1.3.8 firmware from botox.bz I've raised the speed limit to 35km/hr, changed the power constant etc, but my wife still pulls away (although less than before) on her ES4. Changing the speed above 35 doesn't seem to make a difference to my top speed. The other thing is that the power comes in what I would describe as waves, it's not drastic, but I can definitely feel a slow pulse in power (even when using cruise control) than the smooth operation of the stock scooter. Any advice on firmware options to select? At the moment between the giant battery bag and not really seeing the expected results, I'm considering getting rid of the extra battery.