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What you'll need to do is a draw test.
Start by disconnecting one battery cable and setting up an ammeter in between the battery post and cable.
Also connect a jumper wire inline.
Press the lock button on the key fob and let the car sit for about ten minutes to time out.
Then come back and remove the jumper wire, the amount of current flowing will then be shown on the meter.
Anything over about 30-40mA is cause for concern. If draw is higher than that then you'll need to start removing fuses one at a time while watching the meter. If you can remove a fuse and the current flow drops then you can concentrate on components on that circuit.