Buick is Dead, Mom is still alive.
 

I'm new to the Forum, I was just handed down my Mother's 2000 Buick LeSabre Custom with everything on it, it's a very beautiful and well taken care of car in great shape, my Mom is 87, she bought a new crossover something, well I received the car because I like to work on them and I just have a knack for fixing things, so far I have fixed a couple minor things such as a push button headlight switch that the end of it must of melted so it would not spring back, a faulty tire sensor, a right rear power window my bonehead brother decided to take all apart and it was only a switch now I have to replace most of the components that were ruined, one other one was the coils and wires were bad and I replaced those, but the one thing I can not figure out and it has been a problem on this car forever is that it drains and ruins batteries on a regular basis and no one that I'm aware of has been able to figure it out, yesterday I put in a new battery, started right up, I ran it for about 10 minutes, this morning I went to start it and it was dead as a doornail, I would love to hear from anyone else that has had this problem and might know of a solution or fix or if anyone knows why this is happening, I would really appreciate your help!, Thanks for listening, John Sprague, Oshkosh, Wisconsin

Thought I answered this but anyhow. Problem could be either trunk or under hood lamp not shutting off when closed. If those stay on will drain battery, know of instances. Could try removing bulb(s) and see if trouble still exists.

You right, that was was of the problems at one time, my Brother said that it did help for awhile, but now I think it has gone into a serious short from the starter solenoid, security system, anti-theft system, or alternator, Thank you for the response, I appreciate it!, John

Your welcome John, new input is always good. Another thing could be the battery isn't charging enough. An alternator will charge a battery at usually never less than 14 volts, sometimes a few volts higher with a taper down. So one could prove out by running engine and checking VDC at the batt. terminals. Also a battery should maintain at least 12.5 volts when sitting. Cells can go or be dead, if engine turns slow or hard restarting just after it was running is a good indication.

Also a heat soaked starter will be a hard start but doesn't seem to be your problem, work fine with cold engine in most cases.