I have parked my Boxster in the garage for several weeks (since it's suddenly become a brutal winter in the midwest)and locked the car. It has the keyless entry system. Now I am unable to unlock the doors with the keyless and also with the key in the door. The battery in the key appears ok because it flashes when the button is pressed. The interior indicator is flashing as well. The owners manual states after several days the keyless system shuts down and the only way to unlock the car is with the physical key in the door. (But this does nothing).

Anyone have anyideas how to get the car unlocked? I don't want to be using a "jimmy" or coat hanger if I can avoid it due to potential damage.
Is this a battery issue?

Thanks.