Slot 1 and Slot 2 flash carts together?

Thinking about getting both a slot 1 and a slot 2 flash carts. That way i would have the best compatiablity possible.

That and with patches things like the web brower would work using both at once.

On a side note how badly do flash carts drain batteries?

I will probally be doing a lot of testing of the game i am making and dont want to batteries going out on me.

would something like a battery pack help like the folloing ones?

http://www.yesasia.com/?/product_html...ower_Pack.html

http://www.yesasia.com/?/product_html...ding_Grip.html

Has anyone bought from these guys before? There prices are great and so is there selection.

Does anyone know what mah the battery in the ds iis? One says it will power the ds for over 40 hours (on the lowest brightness i am sure)