2004 LCI battery drain - smoking gun?

[audiophool]

So the battery on the old X5 periodically just drains. I can sometimes leave it for weeks, or sometimes the next day it's dead.

Well, this morning I went to start my other car and noticed the interior lights were on. I unlocked the car and switched them off. But when I closed the door and locked it, the lights came back on.

Hmmm.

Another possible symptom is that when the battery has died and I put it on charge, the DS high beam glows/pulses while the battery charges. At that time the charger says the battery is around 4.5V. Solid state charger so I presume the pulsing is the SS charger doing its thing. One time I noticed the high beams were on when I drove up toward the car one afternoon, and yes, the battery was dead.

This battery has been killed more times than Kenny at this point but it still comes back to 85% on load test after charging so I'm reluctant to replace it lest the same thing damage another battery.

With these symptoms, what does the hive mind think?

TIA!!