Fuel Cell Powered Clock

Here is a project I have been thinking about for a while. I've had a Thames & Kosmos fuel cell car kit for a while. And I am collecting a bag full of "dead" batteries to drop off at hazardous waste disposal. My mind started wandering and I thought "I know there is still energy in those batteries, just not enough to run the device they are in, I hate to throw them out while there is still energy in them..." The wheels in my head started turning and I starting thinking about how to drain these batteries completely before disposal while storing and using the recovered energy. First challenge is voltage variation, almost by definition the voltage of these batteries is low and getting lower as they are drained, so that got me thinking of electrolysis to drain them while producing hydrogen which I could then use to power the fuel cell. But the fuel cell only puts out a small voltage, so can't use it to power anything significant - but maybe my 1.5 bathroom clock! So, with all of that in mind, here is my thought process and at the bottom is the final plan.

Basic Car Kit Connections:
This is the connection setup defined in my Thames & Kosmos Fuel Cell Car & Experiment Kit. This configuration uses a solar panel to power the load and power the fuel cell in electrolysis mode to produce hydrogen. When there is no light on the panel, the cell reverts into generator mode and consumes hydrogen to continue powering the load. The book suggests that plastic containers apparently won’t hold hydrogen for long(?) so looking for something glass to use for storage. (book indicates ~50% reduction in hydrogen volume over 12 hours!)

Basic Car Kit Connections - with Bad Idea:
Thought #1 - connect “dead” batteries to the system to remove every last bit of energy before sending for recycling. Problem: book says that the fuel cell needs at least ~1 volt to operate in electrolysis mode, so won’t fully drain the battery. Also, at that low voltage it would become a load for the solar panel and fuel cell (they would try to charge the battery). I think a full battery could be used if a transistor was put in line such that if the voltage of the system drops below a minimum, then the battery is engaged, but that is extra (complicated) circuitry.

Basic Car Kit Connections with Hoffman Apparatus:
Thought #2 - connect “dead” batteries directly to the water for electrolysis. This changes the problem into one of plumbing - the fuel cell needs distilled water, and straight electrolysis really needs salt water to be effective, so the tubing connections need to be done in such a way as to avoid any salt water from getting into the fuel cell. A little Internet searching found "The Hoffman Electrolysis Apparatus", which appears to be exactly what I need.
NOTE: booklet says hydrogen comes off negative terminal of energy source.

Hoffman Electrolysis Apparatus Connections:
Operation, Daylight:
- solar panel powers clock and fuel cell, hydrogen produced is stored in Hoffman apparatus
- battery also produces hydrogen, also stored in apparatus
- when “full”, cathode is out of water and battery electrolysis stops
- continued fuel cell hydrogen produced is vented through center tube

Operation, Night/Dark:
- Fuel cell consumes hydrogen to power the clock
- battery produces hydrogen to replenish
- when water level reaches top, air is drawn from center tube to avoid salt water flow into fuel cell supply tube and electricity production stops (clock stops)