Regarding Vintage fuzz circuits and active pups. There are a number of options for passive pickup emulation, usually in a very small enclosure and not requiring any power of course. I put one in front of my Jext Telez Dizzy Tone and it made a notable improvement in the fuzz response and tone.
Regarding the dying battery scenario, many custom makers have incorporated a starve or bias adjustment in the fuzz circuit, which emulates a dying battery, from a DC power supply source. Starving the circuit usually takes the fuzz from creamy smooth the gacky, sputtering. Often quite cool. This may be a feature to look for in your future fuzz.
Chicago Stomp Works makes some very robust, straight ahead, (unmodified) clones. Their Green Russian Muff circuit is very bass friendly, and while the usual price is under $100, he often has fifty buck deals.
Dr. Scientist Frazz Dazzler
Zvex Mastrotron
These are both readily available and not too expensive.
McSpunckle Gnomeratron VTF
Jext Telez Dizzy Tone V5 or V6
These are not so available, but really cool.
You could spend the better part of the next decade exploring fuzz options, and still not exhaust your possibilities, HAVE FUN!