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Measuring current drain Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Wed, 20 Apr 2005 14:09:59 In Reply to: Battery drain--places to look?, Geza in CA, Wed, 20 Apr 2005 13:07:23 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Your procedure is getting there. Yes, you disconnect one lead of the battery, and put an amp meter (current) in series. Measuring voltage is wrong - you will always measure a voltage (unless the battery is dead).
When you complete the circuit by inserting the meter set to Amps, you will immediately see a large current drain - probably on the order of an amp or two. This is because when you re-connect the battery, various boxes suck up a little power on re-connect. And the dome light may very well come on for a while. So after putting the meter in, wait a minute or two. Make sure all the doors are closed. If there is a button to detect if the hood is open, put a heavy weight on it to simulate the hood being closed.
It is normal to read about 35 - 50 milliamps (0.035 - 0.050 amp) of current, give or take. That's for the clock, radio memory, and remote locking. A car battery in good shape can provide that current for weeks. Now, if after everything settles out you read 2 or 3 amps, then I'd look for a current drain.
How does the battery look? Is it clean or dirty? If it's dirty, wash it with water with some baking soda in it. Batteries outgas normally, and that gas contains acid. That acid condenses on the battery and combines with dirt and 'stuff', to create a conductor. Not a very good one, but one nevertheless. So it can produce a bunch of small current paths between the posts on the surface of the battery - it can discharge itself just sitting there. So a battery wash if it looks dirty is a good idea.
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