06 RRS completely, totally dead.
 

My dad's 06 Range Rover Sport has been acting up. It seems to have been getting progressively worse over the past couple months, but now it is at its worst. The myriad of issues may not be related, but I think there might be a connection.

Recently, we have discovered that the battery had died overnight. We thought this was due to the nav screen being stuck on the Land Rover symbol like it has been doing for a couple months. We put it on the charger and after a good while, it barely has enough juice to crank, but it fired up.

After going into town for a while (about an hour of driving) we stop the car and decide to see if the car would start up. The key goes in fine, turns, but something clicks and it does not start. The green mountain dash light was flashing. AAA came, gave us a jump, and told us that 1 cell in the battery was dead. We replaced the battery, and everything seemed fine and dandy.. It started alright about 3 tines until getting gas later that day. Wouldn't start, needed a jump. Fired right up after receiving a jump. Charged the battery overnight, and the car worked flawlessly for a day and a half.Come the next day, car starts up in the morning just fine.

In the afternoon, we unlock the car. Turning the key, the car doesn't start. This time, absolutely nothing in the car works. There is NO power anywhere. The key turns, but that's it. No lights, no beeps, no dash, nothing. Waiting after about 10 minutes for the jump to arrive we decide to try starting it again. It cranks like normal and starts up, with no auditory indication of a battery drain.
drain. Drove home without needing a jump.

After a few hours of the car sitting (did not charge the battery on the bench), we start the car 3 times in succession, with no issues. On the 4th attempt, nothing. No power anywhere. No dome lights, no security system light, no headlights, no dash lights. The gas gauge is still stuck in position from the 4th try.

This really has us perplexed. Some other unresolved and still-present issues that have started before this event are the radio going completely dead with no sound, no Bluetooth discoverable by a cell phone, amd nav screen being stuck on the LR logo. The only way we can get out of the logo screen and ensure that it turns off is by entering the 753 service menu for MOST diagnostics and turning it off that way.

Thoughts?