The options have been covered to death in this thread but anyway.
You can keep the 18/19 tooth piston and stock sector gear and suffer the fate that 90% of owners get when they throw the junk battery out and get a decent 8.4v.
You can do the above but run with a 7.4v battery.
You could run with a stronger spring but it doesn't get rid of the issue all together.
You could get a normal piston with the 10/11mm spacer (to ajust the aoe), take 3 teeth of the current sector, keep the pre-cocking feature and see how it goes.
as above but get a normal sector gear and loose the