Join Date: Jul 2005
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It's definitely a CR2025 in mine.
The first two digits are the diameter and the last two are the thickness, so it's easy to confuse two CR20xx batteries for each other.
A CR2016 might not make as good contact as the CR2025, though adding a wafer of folded tin-foil to the plain side of the battery might help. Actually, looking at the design of the keycard, a piece of paper would work just as well and would carry no risk of shorting out anything inside the card.
Also, the CR2016 won't last as long as the CR2025 and might not give you the same operating range.
Currently in Horatio's garage:
2010 Laguna III Initiale.