The battery will die from non use. It charges from being in the ignition switch. Sadly you likely destroyed the battery in the unused key from not using it.

There was a guy would replace the battery for $65 if you didn't try to open yourself. Might still exist.

My batteries were about 15 yr old when I replaced them. They were still ok at that point; the circuit board had broken solder joints. I reflowed the solder on both boards and they both worked like a champ for a couple years. I lost one key on a road trip so i eventually bought a new key and then was ok with surgery on the old key. That Became the emergency key anyhow and the new key worked as remote from at least 5x as far away so i was thrilled i bought the factory key and recommend to anybody with m an old diamond key !

My new x5 and wife's F10 both use normal coin cells you just replace when dead. Not sure what possessed bmw to use rechargeable batteries making keys "throw away".


–awr–

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)