[david_connoll]

A weird thing happened to my only key. I opened the gates of an underground car park with a fob, went to the car, and the alarm went off. My key didn't work. Nothing happened when I pressed the buttons. Could the gate fob have interfered with the car key fob signal?
Anyway, I got into the car with the manual door key after panicking because I didn't know that was a thing, then I put the fob in the slot, nothing, no lights nothing, like the battery was dead in the car. Then I sat there watching Drifting FD for 15 20mins on my phone, and bingo key worked, pressed the button and off I went. Bit scared it will happen again, only have 2 weeks not used much.
Any thoughts or advice?

[Ohio Enthusiast]

Might be a bad battery on the key fob. When I purchased my E93 it came with 2 keys, but obviously only one was used and the other one wasn't. The second fob battery was bad, and exhibited the same symptoms - sometimes it would work, sometimes it wouldn't. Remote range was low - you had to be really close to the car to unlock the doors.
When the fob is inserted into the slot in the dash the car charges the battery on the fob, but that doesn't help if the battery is bad, and it takes a long time to fully charge anyway (several hours of driving).
I replaced the battery on my second fob and it works perfectly now.

Do note that replacing the battery requires cracking open the fob halves (it's glued), unsoldering the old battery and soldering a new one in, then gluing the two halves of the fob back together.

The battery type is VL2020 90 Degree terminals. I bought two for $13 from eBay. They are often listed as compatible with BMW key fobs.