I mean, that even with fully charged batteries or running of the charge and play cable, the rumble is much weaker in the wireless controller than the wired one. The wired controller can almost jump out of my hands sometimes with its kick, but the wireless, even when batteries are fully charged, I barely notice it.
I have solved this issue, at least a bit. The wireless controller uses weaker smaller motors that lugs around about 40% less mass than the wired ones. So I simply installed the motors from a wired controller into the wireless one. Though, since you have less voltage, it does not get up to the same speed as with the wired controller, and this will also eat a bit more battery time, it is noticeable the difference between the default motors and the ones that came from wired controller.
Unfortunately this had an additional issue, weak rumblings are now not felt at all... Guess I will have to play around with this until I get something that is ok.
UPDATE: My conclusion is that it would take a charge pump to increase the DC voltage to around 5-6V and some modding to feed that voltage only to the motors when necessary.