Keyless Entry works on/off
 

So, I tried doing a little research here first but couldn't find a solution or similar problem.
We have a 2003 BMW X5 with 2 original keys. Brand new battery installed one year ago. Recently, an interior light and dashcam were left on and drained the battery, but not to the point where it wouldn't start (but very close).
Afterwards, my wife (primary driver) informed me that the keyless entry no longer worked. I tried it and confirmed. Performed a key reprogram for both keys and received successful indications from the car. Tried a key and it worked fine for lock/unlock but not the other key. So, we left that one and stayed with the one that worked, but my wife said it works almost every other day. But, trunk release works all the time.
Problem developed when the battery drained low and now only works half the time. What can I look into? What could be causing the keyless entry to work one day but not the next?

When mine did the same it was the key. Replaced the key and life was good. A new factory key at ≈ 17 years old was my favorite upgrade.

I thought it had to be car side like problem with the receiving antenna.

Others have said they had similar situation.

If the trunk opening works without a problem it must be just failing micro switch for opening on the remote.

When i refurbished my switches reflowing the solder joints on most connects brought them back to life fire a couple years. Then i lost one key on a vacation. (fortunately had wife bring her spare so we got home) then that one failed again with similar symptoms as above. New key was 100%

You can use BMW Scanner to see when the car thinks it is receiving a signal. I don't remember if a Foxwell will tell you that.



However I think the trunk release uses the same communications module (the FZV antenna behind the rear spoiler) as the keyless entry, so if that works it would indicate a key side problem. There are a few folks out there you can send the diamond keys to, who will fix solder issues and replace batteries for like $50/key (instead of $200 for a new one).

Yes. Same communication for all remote controls. Antenna amplifier receives and sends the message to body module (GM).

There are simple battery check testers at some stores that will light up an LED when you press a button on your remote. You can test if each button will work. You need the lock and unlock buttons to both work at the same time to sync the key to the car.

So, brought both keys to a shop and they tested the keys as working fine. I opened them up, changed one battery with a new one and checked to make sure the contacts are clean and making contact. Problem still persists. My wife's theory is that something happened when the battery was drained one night because she's certain it's been happening since then. I brought the battery to the company I brought it from and they tested it as fine.
They said it was at 89% charge and it seemed a little low. Put the battery back in and checked the charging voltage at the battery terminals. it was reading between 13.8 and 13.9. My van with a new alternator and 2 yr old battery charges at 14.3v.
Doesn't seem too far off but it is off enough that it could be making the car unhappy? should I be looking into replacing the alternator? any other ideas?