Hi all! Need some info on the back lift gate on my 2012 Nissan Quest. Worked fine until a few months ago when I had to have the alternator replaced. Immediately afterwards, I discovered the gate would not open from the outside, and when I pressed the key fob to lock/unlock the doors the gate did not respond. However, it opened manually from the inside if someone crawled through and released the lever. Lived with this until a few weeks later, when I accidentally ran the battery down and used my jump box to jump the vehicle off...after having a dead battery the lift gate went back to working almost as normal again - it would open from the outside, key fob unlocked and locked it, etc. Only issue was that the "self-closing" feature that pulls the gate completely shut once you gently close it wasn't working, but hey, I could live with that. Worked fine for about 2 weeks, and then quit again. It still opens manually from the inside. Anyone have any idea how to fix this? I really don't want to take it to Nissan and be charged an arm and a leg for a repair.

Welcome to the club of those who are affected by Nissan's atrocious quality of electric and other components.
Nissan is Japanese for a "difficult to troubleshoot intermittent failure, which, for a dealer's staff, is almost impossible to reproduce". Look in the dictionary if you do not believe me.
It can be anything from wire harnesses to relays, switches, sensors, BCM, etc.
Your best bet would be to download the FSM and see if there are troubleshooting steps you can follow with a multi-meter.

Maybe not that hard. Devices like that have limit switches to tell the motor when to cut off, get out of adjustment and they quit working at all.

Like said, the service manual and see what it takes just to test the motor when gate is open for working, if motor works then likely a switch acting up there. If you wait for NIssan techs to do that the car will be in the scrapyard before they likely fix it. I learned to go into Ford door latch assemblies to fix them permanently for pennies at $150 cost saved for each and another $400 to change them. Ridiculous. Same on the tailgate latches and electric window regulators on those as well.

Why I don't buy cars with extra add-ons like that if it can be avoided, they simply mess up left and right, Nissan not well known for super reliable electrical. Manual gates simply do not break. Wait until Nissan gets overwhelmed by all the lane keeping and collision avoidance stuff messing up to cause lawsuits, them putting all that crap on the cars is justification for the suits and they haven't grasped that yet. It has already begun.