first time lapse, tips?

[theregoesjb]

I am thinking about trying my first time lapse, im going to build a dirt pump track out back in the woods and thought it would make a good video. It will likely take a few days so i am thinking ill just mount an extra tripod head to a board and screw it into a tree or something similar.

I have a canon t2i with 32gb SD card, i looked into the price for an intervalometer and saw the Aputure AP-TR1C for 30-40$. That alone made me think i might as well try. I am wondering about battery power though, How long could i expect to shoot for with 1 battery. I started looking at battery grips so i could have two going at once (i already have two [FONT=Lucida Grande, Arial, Helvetica, sans-serif]batteries) but i wasnt sure if i needed it or if maybe that still wouldn't be enough..

I know battery consumption is somewhat dependent on the settings of the camera for the time lapse but since im new to it I am still not sure what ill do for settings. It will be daytime and i expect to have a good amount light, ive seen conflicting information on auto-white balance.If i wanted to fit 15 - 20 hours into a few min of time lapse video how would i figure how often to shoot?[/FONT]