In the summer my car starts fine…however in the winter I have to dissconect the battery at night or it will go dead. I have no lights or anything turned on that should be draining it. The shop says it all checks out fine though.
Get a meter and find what is drawing the current. Something is.
79 Corolla… is there any chance this is still a really nice car? It could be so many things causing it to drain. If the mechanic cant find it, and you cant find it, heres what Id do (and have done before). Get a key-turn style battery cutoff switch that you can wire inside the car. I got mine off ebay and it came with about 10 feet of each wire lead. I made a bracket and mounted it under the dash. Cheap and easy fix for a car that still ran great otherwise.
Me thinks the battery is bad. The warmer days of summer are better for marginal batteries that the cold nights of winter. Most battery problems occur in colder temps. Have you tried replacing the battery?