I would go with a maxamps 6000 7.4v battery. They fit right into your cars with no mods and have lots of run time. I have been running my 6000 since Febuary and it still has the same amount of power and run time as when I first ran it.
I also use a dura-trax ice charger it is very easy to use and the price is not bad ither.
Hope this helps,
David