QuestionI have a 1991 Mercedes Benz 190 e 2.3 with about 250,000
recently i have been experiencing problems with my vehicle i have replaced both the alternator and battery but my car continues not to hold any type of charge i constantly take my battery to the local auto store for charging and constantly get the same answer that its a good which is puzzling seeing that i just had my alternator replace and the battery is not holding a charge for longer than 3 days.........can you please give me any type of knowledge to why this problem is occurring and any solution that is not very pricey.......thanks
AnswerDebro,
There are several possiblities for causing battery drain. If the alternator has a bad diode it will allow back flow from the battery to ground, or if the voltage regulator is bad it can cause problems as well.
If you have a volt meter, or can borrow one, you should be seeing about 3 volts plus or minus .5 volts while the engine is running. A bad diode would not show up here. Bad ground to the battery or other grounding places, could cause the same issue.
The battery could check ok and still have an internal short that would cause it to drain over time. I had a Mazda that would completely stop when I made a right hand turn. I eventually traced it to an internal short in the battery.
Remember the battery is for starting and storage only. While the vehicle is running, the alternator is suppose to provide all the amperage for all the things being operated on the car while keeping the battery full. This is the reason for having 13 volts coming to the battery while running.
Here is some additional info I located on the web, and it says it pretty well.
We know your alternator is charging or the car would die w/running after a few min. We also know that the battery is LOOSING its electricity over a period of time. With this thought there is only one way a battery can loose its electricity and that is a short by completing the circuit between neg and poss terminals such as you do when turning on your lights via a switch, or opening a door and allowing the button to complete the ckt for the interior lights, etc.
There are only a couple ways to complete the circuit to eventually kill the battery of limited stored electricity: One is to have an internal short in the battery where it kills itself. This can be tested by allowing the battery a chance to charge as you did by letting the alternator run and charge the battery, then disconnect at least one of the battery terminals and let it sit. Next morning reconnect and see if it still has charge. If so the short is in the second possibility which is the vehicles electrical system. If no charge then the battery is to blame. Now, getting back to the second possibility of the electrical system having a short and bleeding electricity from the battery over time: You can test for a short by putting a test light between the battery post and a DISCONNECTED terminal from the same post. If there is a light then you have a complete circuit somewhere and this is bleeding the battery down over time. (Dont forget to disconnect the hood light and close all the doors so as not to bias your test). If the test light is on confirming a complete ckt within your vehicles electrical system then pull fuses out of the fuse box one at a time at the same time checking if your test light goes out and replacing the fuse before pulling another so you wont forget where it went orig. If the light goes out upon the removal of one of these fuses you can look in your owners manual and see what this circuit supplies then limit to these components. Now if you would like to go further for identification you disconnect each of these components noting if the test light goes out thus finding the culprit.
Some tricky hints: Glove box open enough to keep light on or glove box switch not shutting of its light, trunk light staying on, courtesy lights switched to stay on regardless of doors being shut or not, hood light staying on w/shut.
Good Luck and let me know what you discover.
Robert
