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Recently I left my 2006 Xtrail lights on and flattened the battery. I then connected jumper leads from my wife's car, and my car's engine turned, but failed to start. I called the NRMA, and the serviceman connected his jump-start unit, with the same result. He then asked me if I had a spare key, which I did, and which started the car. Neither key has any buttons, they are attached to separate dongles having the usual lock, unlock and horn buttons. The serviceman then showed me a trick: he inserted the "Good" key into the ignition socket, started the engine, partially pulled the "good" key out of the socket and touched its metal prong with the prong of the "bad" key. He then changed keys, and the “bad” key started the engine. The battery was replaced. Some days later, I absent-mindedly inserted the "bad" key and unsuccessfully attempted to start the car. Can you satisfy my curiosity with a simple technical explanation please? Should the “bad” key be replaced, and is the “good” Key due for replacement? Thank you, Tim.