# Car batteries and damp weather **URL:** \ **Category:** Factual Questions\ **Created:** [October 19, 2000, 9:01pm UTC](https://boards.straightdope.com/t/car-batteries-and-damp-weather/37580 "2000-10-19T21:01:36Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![Johanna](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johanna/32/8318_2.png) [@Johanna](https://boards.straightdope.com/u/Johanna)\ **Post date:** [October 19, 2000, 9:01pm UTC](https://boards.straightdope.com/t/car-batteries-and-damp-weather/37580/1 "2000-10-19T21:01:36Z")
I replaced my car battery today. The old one would die whenever the weather was damp. I’ve noticed this with other cars too. How come the wetness makes the battery dead? What can you do about it (besides replacing the old battery)? ---
**Author:** ![Bottle\_of\_Smoke](https://avatars.discourse-cdn.com/v4/letter/b/b9e5f3/32.png) [@Bottle\_of\_Smoke](https://boards.straightdope.com/u/Bottle_of_Smoke)\ **Post date:** [October 19, 2000, 9:13pm UTC](https://boards.straightdope.com/t/car-batteries-and-damp-weather/37580/2 "2000-10-19T21:13:09Z")
Just a WAG here, but… Odds are that it might not be your battery, but rather the battery connectors or some other part of the wiring. If you have frayed wiring, sometimes the wires will arc in damp weather, robbing the starter and/or plugs of power. You can test this by opening the hood with the car running and spraying a mist of water around the engine, looking for sparks. ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [October 19, 2000, 9:22pm UTC](https://boards.straightdope.com/t/car-batteries-and-damp-weather/37580/3 "2000-10-19T21:22:54Z")
Another possibility, if your car is old enough, is that you have a cracked distributor cap. Moisture inside the cap is one of the easiest and surest ways to disable a vehicle with a distributor. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [October 19, 2000, 9:30pm UTC](https://boards.straightdope.com/t/car-batteries-and-damp-weather/37580/4 "2000-10-19T21:30:25Z")
> [@](#): > > \*Originally posted by ishmintingas \* > \*\*I replaced my car battery today. The old one would die whenever the weather was damp. > > I’ve noticed this with other cars too. How come the wetness makes the battery dead? What can you do about it (besides replacing the old battery)? \*\* I’m at a loss as to why that would happen. Is perhaps your battery (or an exposed V+ somewhere on the car) getting soaked by water when it rains, thereby providing a low-resistance path between V+ and gnd and thus discharging it? ---
**Author:** ![Foaming\_Pipe\_Snake](https://avatars.discourse-cdn.com/v4/letter/f/958977/32.png) [@Foaming\_Pipe\_Snake](https://boards.straightdope.com/u/Foaming_Pipe_Snake)\ **Post date:** [October 19, 2000, 9:34pm UTC](https://boards.straightdope.com/t/car-batteries-and-damp-weather/37580/5 "2000-10-19T21:34:24Z")
Smoke’s got a point. On that PBS radio show Car Talk they were talking about how changes in humidity and moisture can make battery cables expand and contract, screwing up connections and making spark plug contacts poor. Granted, cold weather will also weaken a battery’s charge. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [October 19, 2000, 10:04pm UTC](https://boards.straightdope.com/t/car-batteries-and-damp-weather/37580/6 "2000-10-19T22:04:56Z")
> [@](#): > > \*Originally posted by Foaming Pipe Snake \* > \*\*Smoke’s got a point. > > On that PBS radio show Car Talk they were talking about how changes in humidity and moisture can make battery cables expand and contract, screwing up connections and making spark plug contacts poor. > > Granted, cold weather will also weaken a battery’s charge. \*\* I understand what the Car Talk hosts are saying, but ishmintingas seems to be implying that his/her car battery is “dying” prematurely. A bad connection usually increases circuit resistance. This will not discharge a battery, but instead will make it more difficult to start the car (if the problem is in the high current starting circuit). And I fail to see how a new battery will solve that problem. (In a situation where you have bad connections, a new battery _might_ help a _little_, since it will have lower internal resistance.) I have had my share of battery problems. I have found that today’s batteries are quite reliable unless you accidentally discharge them. Completely discharging a car battery just once is **very** bad on it. And if you discharge it twice you’re better off just turning it in and buying a new one. ---
**Author:** ![Johanna](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johanna/32/8318_2.png) [@Johanna](https://boards.straightdope.com/u/Johanna)\ **Post date:** [October 20, 2000, 2:20am UTC](https://boards.straightdope.com/t/car-batteries-and-damp-weather/37580/7 "2000-10-20T02:20:58Z")
I still don’t know exactly what the problem was (the negative pole on the old battery had that accumulation of light blue powdery crud), but all I know is as soon as I put the new battery in, the car started up very beautifully and efficiently, crisp and clean. The difference was very evident. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [October 20, 2000, 2:58am UTC](https://boards.straightdope.com/t/car-batteries-and-damp-weather/37580/8 "2000-10-20T02:58:49Z")
> [@](#): > > \*Originally posted by ishmintingas \* > \*\*I still don’t know exactly what the problem was (the negative pole on the old battery had that accumulation of light blue powdery crud), but all I know is as soon as I put the new battery in, the car started up very beautifully and efficiently, crisp and clean. The difference was very evident. \*\* Sounds like your battery was simply bad. How old was it? If it was over 5 years old, it was probably on its last leg. Is your alternator adequately charging your battery? Start up your car and check the voltage across the battery; it should be somewhere between 13.5V and 14.2V. Another possibility is that your old battery was good, but you had a poor connection at the battery posts when it was in the car. When you installed the new battery, the connection was much better (cleaner and tighter). This probably wasn’t the case, but it is still a possibility. ---
**Author:** ![handy](https://avatars.discourse-cdn.com/v4/letter/h/b5a626/32.png) [@handy](https://boards.straightdope.com/u/handy)\ **Post date:** [October 20, 2000, 3:32pm UTC](https://boards.straightdope.com/t/car-batteries-and-damp-weather/37580/9 "2000-10-20T15:32:41Z")
YEah, make sure those connections are tight. If you grab one & twist & it twists, its not tight enough. Often, you have to put on a new bolt to make sure its tight. ---
**Author:** ![casdave](https://avatars.discourse-cdn.com/v4/letter/c/c6cbf5/32.png) [@casdave](https://boards.straightdope.com/u/casdave)\ **Post date:** [October 20, 2000, 10:36pm UTC](https://boards.straightdope.com/t/car-batteries-and-damp-weather/37580/10 "2000-10-20T22:36:50Z")
Batteries get plain worn out but humidity can affect the HT leads and coils too. If the battery is in good condition this probably has little effect but when things get worn out it doesn’t take much, just a collection of cumulative problems to stop things operating smoothly. ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [October 20, 2000, 11:11pm UTC](https://boards.straightdope.com/t/car-batteries-and-damp-weather/37580/11 "2000-10-20T23:11:29Z")
> [@](#): > > \*Originally posted by KneadToKnow \* > \*\*Another possibility, if your car is old enough, is that you have a cracked distributor cap. Moisture inside the cap is one of the easiest and surest ways to disable a vehicle with a distributor. \*\* I can attest to this one being more common than you would think. I absolutely **amazed** my grandmother when she told me that her car wouldn’t start, and her battery was almost dead from trying. I knew it had just turned cold and rainy that very morning after an extended dry spell, and I went over, pulled the cap, wiped the water out, and it started right up. It took all of 30 seconds to do. She was so proud of me. 🙂 ---
**Author:** ![handy](https://avatars.discourse-cdn.com/v4/letter/h/b5a626/32.png) [@handy](https://boards.straightdope.com/u/handy)\ **Post date:** [October 21, 2000, 2:59pm UTC](https://boards.straightdope.com/t/car-batteries-and-damp-weather/37580/12 "2000-10-21T14:59:41Z")
“pulled the cap, wiped the water out” Time for a new cap, one that fits better. I saw a guy squirt wd-40 inside instead of wiping it. You get a little POOF! when start it doing that… ---
**Author:** ![chique](https://avatars.discourse-cdn.com/v4/letter/c/4491bb/32.png) [@chique](https://boards.straightdope.com/u/chique)\ **Post date:** [October 22, 2000, 1:18am UTC](https://boards.straightdope.com/t/car-batteries-and-damp-weather/37580/13 "2000-10-22T01:18:26Z")
Trust me, it’s not the battery alone. First I thought it was my fuel filter making my car run funny (especially when I took it off and found the filter itself had disconnected from the walls). It didn’t help. When my car failed to start a few weeks later I replaced the battery. Car ran fine for about a week, then failed to start AGAIN!! I had my car towed to the shop (thank the IPU for AAA!), had my wires and cap replaced, and haven’t had a problem since. Except for when the fuse running my fuel pump blew :rolleyes: