Yesterday my 52 L322 M62 wouldn't unlock after dropping the kids at school, it had been fine before hand, started without issue. I tried the fob first, nothing, so assumed the fob battery had died so tried the key, the drivers door unlocked but no central locking or indicator flash. I should have checked the red alarm light but didn't think of it. At this point, I'm guessing the car battery is flat so got a lift home for jumper cables. When I returned about a hour later, the fob unlocked it without issue and it started first time. It's been fine since. I've checked the battery terminals, they look fine, I had the battery tested at Halfords, they say its fine. Other than waiting for it to happen again, is there anything else worth doing?

Earthing straps to the engine are favourite for these sort of things os front lower to chassis is a good starting point