Please help, I don't have an owners manual and I can't find the battery

Dear jd--  According to Mason in the service department of John Elway Pontiac-Buick in Lone Tree, Co., the battery for your 2000 Buick Lesabre is under the middle of the back seat.   Good luck from Bovan.

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.