The other night, my flatmate Dan’s car alarm remote died, and we couldn’t find anybody who was open that stocked the right size battery – we needed a 12 volt A27 size battery, the best we could get was an A26, which is too fat to fit in the remote.
So here’s a couple of pics of the scheme that I devised…


We took the next 12V battery we could get, and cellotaped some wires to it. We then twisted the other ends of the wires around the battery contacts of the remote, and wedged the old battery in to make it snug. Voila, one working car remote with external power-supply.