E46Fanatics - View Single Post - replacing battery in key fob....
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Old 06-13-2012, 08:18 PM   #372
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Join Date: Nov 2010
Location: Sacramento CA
Posts: 266
My Ride: 2000 323ci
Originally Posted by djarndtsfo View Post

i too needed to replace one fob's battery and found this thread and it was very helpful. I was able to open up the key fob and unsolder the battery and was about to order the horizontal battery from mouser or digikey. Before i did, i researched the battery on the panasonic battery site and found that another non-rechargeable is essentially the same size and voltage. I picked one up at my local drug store (2025 or equivalent). Now, here is the part that you may or may not want to try (see picture). After removing the battery, i used needle nose pliers to roll the welded tabs off like you do to open a can of sardines (those who remember using the included key to remove the metal strip around the can). I then smoothed them back out flat and soldered both battery contacts back on without the battery (you may actually trim off the battery contact wrinkly part if you want). This makes like a slip-in battery holder. I slipped in the battery, wrapped a rubber band around the fob and tried it. It works great! Yes, i know this is not a rechargeable, but i could not find anything on the circuit board that takes an outside electrical source that could possibly recharge the battery (i will do some more research, but i don't think it has to be a rechargeable type battery). The only other significant difference between the rechargeable and the 2025 lithium i used is a specification for nominal capacity (mah). The rechargeable is lower at 7 as opposed to the 2025 which is 165 mah which means it should last longer! Well i have been using mine for a total cost of less than $3 now for over 7 months and it's still going strong. Just in case though, i used a silicone sealer type adhesive that is strong but removable if i have to change the battery. The beauty is that if there is a next time, i just slip out the old battery and slip in a new $3 battery and reseal (no more soldering). The plastic holder the fob has for the battery space puts enough pressure on the slip-in cell so you don't have to use the solder variety. Hope this helps - good luck. Donald (electronics engineer) san francisco.
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