I want to say it's in a really strange place like under the back seats or in the trunk maybe. I can't remember. Quick call to a Buick dealer and they will be able to tell you.
The battery to you Buick is under the rear passenger seat. If you put your fingers between the seat itself and the back rest and pull outwards it will "pop" out. There will be the battery under the seat. If you replace it make sure not to discard the rubber tube that connects to the battery. This vents to gases produced the battery to the atmosphere. I would jump the vehicle from under the hood and drive it around to fully charge the battery before replacement. The positive jump terminal is on the passenger side under the hood. It is connected to the fuse box and has a red plastic cover over it. A good ground would be anything without and paint on it. Hope this helps.
Search Buick LeSabre Questions
Buick LeSabre Experts
Related Models For Sale
Used Cars For Sale