'96 Volvo 850 battery drain

I have a have a 1996 Volvo 850 non-turbo. For the past year I have had a problem of the battery draining itself over night. I took it in to a mechanic and they said the battery and alternator and everything was fine and they could not find the drain. It will only do it in the summer. The car would be dead 3 or more times a week and would easily jump start. During the winter it did not do it at all. Then as soon as it started to get warm and humid out again it started all over. Currently I just unhook my battery after using it. It would drain the battery over night.

I figuring it is some drain related to humidity and rain fall but i do not know. Anyone have any ideas so i can fix it, thank you

This may be too far out, but if your car has a trunk light or under the hood light controlled by a mercury switch, this might be the problem. Mercury used to be used in thermometers and would expand as the temperature increased and give a higher reading on the thermometer scale. Try removing the trunk light bulb and see what happens.

My Dad had a 1973 Oldsmobile that had a current drain that would run down the battery if the car sat a couple of days. A couple shops couldn’t find the problem. I finally discovered that the light in the center console was staying on. I just happened to be examining the car at night. The problem was intermittent–sometimes the switch would stick and sometimes it wouldn’t. At any rate, I would remove the bulbs in the glove compartment, console, underhodd and trunk and see what happens.

You Volvo owners sure are a funny lot. So, let me get this straight; every day you drive home, pull into your garage or parking space, shut off the engine, open the hood, and disconnect the battery.

Is that correct?

And you think this has no effect on your car’s radio, security system, or anything else?

Are you kidding?

Battery drains are not related to humidity, weather, or any other meteorological activity. They are related to mechanical malfunctions. Either the battery is weak, the charging system is weak, or there is an open circuit somewhere. Maybe all of the above.

It cracks me up that you’ve been putting up with this for a year. As I said, you Volvo owners are a funny lot.

Here is a link to help you see how the testing is done.