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Old 02-18-2013, 02:39 PM   #7
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Join Date: Aug 2008
Location: Torrance, CA
Posts: 2,624
My Ride: '99 323i & '02 540i
Originally Posted by Surrept View Post
Umm. You wouldn't have to reprogram the key if you replace the battery. That doesn't even make any sense. I replaced the battery and all of my key functionality resumed as normal. You aren't changing the circuitry, just the battery.

EDIT: Also when I purchased a replacement battery for my key, I do remember the website stating that those batteries are good for 1000 charges. So you can't charge them forever and it may be time for a replacement.
If power is removed from the key fob circuit for a short enough period of time the capacitors can keep the rolling code position alive so that resyncing is not necessary, but, that is not always the case and resyncing will be necessary to get back the remote functions.

I'll quote from the battery data sheet, "Approx., 1000 times at 10% discharge depth to nominal capacity." Since under normal conditions the battery is never discharged anywhere near that deep they will last much much longer. 10+ years is not a problem. I repair a lot of keys and I only have to replace the original battery when the customer has f'd it all up following that idiot on YouTube that says to break the leadframe off the battery at the weld points.... If the battery hasn't been dicked with I just repair the key, close it up and send it back with the original battery. The original battery always measures between 3.1 and 3.3 Volts and brand new batteries measure only 3.0 Volts since they don't come from the factory fully charged.

Last edited by scottjoh; 02-18-2013 at 02:40 PM.
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