The Lithium-Ion batteries, unlike Nickel-Cadmium batteries, have no "memory effect" which can reduce the usable power of the battery over time.
The BP-945 4 500 mAh lithium ion battery pack will work with the Canon Canon XL1, XL1s, GL1, GL2
Optura, Ultura, Elura, ZR, and Vistura (with CH910)