Disconnecting the battery?
 

I need to work on the alternator on my E70. Any reason to not disconnect the negative lead on the battery?

You will not be able to open the lift gate with the battery disconnected. There is a manual release but I couldn't find it personally.

Don't you need to have the lift gate open in order to get to the battery in the first place?

Yes, but if you don't have a garage and it rains while your doing the work, you are probably going to close it. I did.

1. if you don't lock the doors and the battery is disconnected and the tail gate gets closed...you can always open the hood and connect a battery charger or other power source to the jump start terminals. This should supply enough power to unlock the tailgate.

2. if you have the battery disconnected and you have a need to shut the tailgate AND lock the doors...can you manually lock the doors in the e70? If yes, then single lock the vehicle (done by manually locking the doors or using the central lock button just prior to pulling the battery cable) using one of the passenger doors as your last exit. You can then MANUALLY unlock the driver's door with your key blade, then access the interior to either manually unlock the tailgate...or use the jumper terminals in the engine bay to supply electrical power.

All of the doors were unlocked, the negative cable disconnected and attaching a charger, a battery or a battery AND charger to the underhood terminals provided zero power for anything in my case.

You can lock and open the other doors with a combination of manual operation and the key blade without the battery connected.

Here's my 2 experiences. I report, you decide:
1. Had to replace battery, did a quick swap in the parking lot -> 0 problems.
2. Had to replace camera cable, decided out of precaution to disconnect the battery -> fried FRM module, ~$300 damage (could be worse, luckily FRMs were cheaper back then and did the coding myself), and much appreciation of the irony...