They all suck. Nikon, Canon, any digital. The whole camera runs off the battery, unlike a manual where they can last for years.
I have the battery grip for my D200 that holds 2 batteries. I have a total of 4 that I keep charged all the time. Gets me at least 2 days of heavy shooting before re-charging. I don't know if they make a grip for the D40 or entry level Canon. I would doubt it.
1999 e46 328i Ti Silver / Black[retired]
2007 e90 335xi Jet Black / Black[retired]
2011 e70 X5 35d Vermillion Red / Cinnamon
2011 e92 M3 LeMans / Fox Red extended