I'm having a problem with my key remotes on an E-39 535ti.

One key fails to open the doors at all.
One key opens the doors ok, but does not activate any of the
adjustments.

For a few days last week, both keys started working properly again.
Now they are back to the problem as descirbed above.

Far as I know, these keys recharge while in the ignition, so it's not
batteries, correct?

If they are charged, what else could it be. Is there an antenna issue
where the signal is not being perceived?

Thanks to anyone who would be so kind as to point me in the right
direction for solving this problem.