I am staying in the the Marais near the Bastille and need a Canon camera battery in the worst way. Any recommendations are apprectated. Thanks for the help.
Carrefour Express. The closest is probably across the river about even with the cathedral, about two blocks in on R. Lagrange. If there's a closer 7-11 type joint (Monoprix, Franprix, et) stick your nose in there. Stop in any phone shop along the way.
There's a Darty at Republique, 1 avenue de la République which opens on Monday at 10:00 if you haven't found anything by then. Closed tomorrow of course.
Have you tried Googling a camera store?
Any of the FNAC stores will have them. Just go to the camera department.
FNAC next to the Châtelet - Les Halles station where you probably got off the train from the airport. While there you can buy a pass to the Lourve and avoid the ticket line.