Freelander 2 (LR2) SatNav & radio pulsing On/Off

Weird one this. A week or so ago I couldn't find my car keys so dug out the spare fob that hasn't been used for over a year. Plugged it in and the car started no problem; everything as normal.
After driving for about a mile I put the radio on and that's when I noticed the SatNav display was going Off and On at approximately 2 second intervals. Weirder still, so was the radio. The CDs wouldn't play at all. No fault lights on the dash and no warnings on the display.
I arrived at my destination about 40 minutes later with the display still turning Off and On every couple of seconds and wondering if this was going to be the start of something serious.
A couple of hours later I got back in the car and everything was back to normal. SatNav display okay, Radio okay, CDs played okay (6 x 130 MP3 files) and phone connected via Bluetooth.

I can only assume the keyfob battery was flat, or nearly so, and the display behaviour was the car's way of letting me know. I fitted new shells and batteries to both fobs a couple of years ago, but have only been using one of them.

Those symptoms are normally the first signs that the BT module is failing. However maybe it had some damp on the MOST data link, causing the issue.

It will have been the security seed was out of acceptable range (i.e. time since key last used), usual fix is to leave key in ignition 20 mins, remove key, lock car for >3 mins, open car & insert key. All fixed.
Basically the key passes the hardware security but the theft relevant modules don't recognise it's 'password', leaving it in the ignition allows a re-sync, taking it out & reinserting updates the security seed in the vehicle.