PaigeTrain,
I bought my toddler the Lionel Crayola G scale train set (same as the Polar Express, just Crayola paint scheme). I too found out that the 6 C batteries last a few days then die on you. I realized that replacing the batteries would get expensive really quick so I bought the following at Hobbytown in Dallas:
* Battery - dynamite (brand) 600mAh 9.6 Ni-Cd Pack (about $15 if i remember right)
* Battery Charger - ONYX 110 AC/DC Peak Charger Model #DTXP4191 (about $20, also if I remember correctly)
It takes about 30 minutes to recharge the battery. You could probably find those cheaper on the web but I didn't want to wait
Ps.. The Crayola G scale set I bought was the best $69 I ever spent. My toddler plays with that thing every single day for at least an hour. I even bought him 2 sets of expansion track to extend his "layout".