I started wondering "How would one make the initial charge for the PMH without a generator or a manufactured car battery?" This led me to cement, earth, water/saltwater batteries and finally, crystal batteries. The main reason these have caught my attention is because their lifespan seems to be off the records (some have claimed to run LEDs for 2+ years and motors for 6 months before just shutting them down). Others have had 6 motors at a time running off earth batteries, so it makes you wonder what is possible when connecting a ton of these in series (for more voltage) or in parallel (for more amperage).
Crystal batteries are basically any kind of crystal (Salt, sugar, alum, borax, etc) grown around 2 disimilar metals used for 2 electrodes to produce current (from my research and experiments, aluminum is good enough for - and copper is best for +). I'm not so sure about salt, as it might corrode metals, but what I'm basically talking about are alum/borax type crystals.
The corrosion of the metals seems to be nonexistent, as opposed to water batteries or saltwater batteries, and there are debates over whether this is the common galvanic reaction found in most batteries. There are also a few researchers who have used gel-like substance with metals and noticed the corrosion took a much slower rate. This might mean that the structure of a crystal has the same effect as water batteries but without the corrosion.
I'm not sure if many people are familiar with them, so I'll explain briefly some key points:
John Bedini and John Hutchison has worked on them (they are also called "Hutchison cells") more than anyone else, I think.
There are a few youtube channelers who are really doing some amazing work (lidmotor, ibpointless and lasersaber stand out).
Check these out:
Literal Crystal Battery Running a Pulse Motor
Polycrystalline Literal Crystal Battery
(notice the voltage goes from 0.55V - 0.51V then back up and down again, then later on it goes from 0.54 to 0.57 then between those ratios)
The Hutchison Cell
(Ignore him dancing in drag queen outfit and pay attention when he says "this is the solution to the energy crisis, in my opinion". Maybe he's right?)
12V Earth Battery
Crystal Cell Running Magnet Motor 2+ weeks (before he took it down)
Earth Battery Runs Six Motors Continuously
Growing Alum crystals is fairly easy: