Hello, I have a Epiphone Prophecy SG Guitar ( http://guitars.musiciansfriend.com/product/Epiphone-SG-Prophecy-Custom-EX-Electric-Guitar-with-EMG-8185-Pickups-?sku=515622 ) I'm planning on changing out the Neck Pick Up for a better clean sounding pick up. Right now it has a Active EMG 85 pick up in the neck posistion. I'm going to put a passive pick up in place of the Active one. I have never changed a pick up like this before. Do I need to do anything different because it is an Active Pick up apart from just dissconnecting it from the battery? If only my Bridge Pick up ( EMG 81 ) is Active, does that mean it gets double power from the battery? The more detailed the answers, the better. Thank you.
It's... difficult... to run actives and passives at the same time. They require different pot values
ProTone Pedals: Attack Overdrive
Fractal Audio: AxeFX 2
Engl: Fireball 60
Zilla: Fatboy 2x12
Carvin: DC700
Carvin: Vader 7
Schecter: KM-7 MKii
Schecter: Banshee 8 Passive
Jackson: DK2M
for cleaner sound turn down the volume on the guitar
now for your answer...

you cant have active and passive pick ups in a guitar
well you can but its more work than its worth honestly.
now disconnecting one pickup wont give the other double the power

and if you want to go passive you might want to go full passive which means you need to replace the pots in the guitar to different values
Your best option to get better cleans out of that guitar is to put an EMG 60 in the neck position. It has better cleans than the 85 and since EMGs have the quick connect on the back changing them out is very easy. No soldering at all.

If you go passive you'll have to change almost all of the electronics that are in the guitar now. I think I'd try the EMG 60 first.