I never charge my Tx at home, it has a USB port which is charged from the USB port on my charger at the track, typically gets topped off in about an hour and I will top it off between rounds throughout the day.

The track in our area will run the lower mains first, so if someone gets into a bump situation, then there's no problem getting their battery charged before the next main assuming they have a 40A charger, no need for a second pack. This is a justification for buying a higher quality charger and higher quality battery that can handle 40A charge rates so you don't need the added expense/hassle with maintaining more than 1 pack per class.

I also run 3 classes with a 2 port charger, typically have the first pack already finished charging by the time I finish racing my 3rd class and need to put that pack on the charger