How should the Magic market be regulated?

Question

Context

Wizards built a civilization on a barren planet.
More details here.

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Magic Batteries

The population of the planet is between two and four million wizards, but not all of them are born equal. More than half of the population don't produce enough magic, or lack the focus, to actually cast spells.

They still produce some magic, that can be harvested and stored in magic batteries. The collected energy can be used to power things like sentient automatons/robots, flying boats, atmospheric spells, etc.

To charge a battery, people have to carry it around with them, see illustration bellow (pardon my poor drawing skills).

Depending on the person, a battery can take from a few hours to a couple of month to charge. Once fully charged, there's no difference between them, no matter who charged it. If not damaged, batteries can be used and recharged indefinitely.

The battery market

I still don't know how to regulate de battery market.

My goal is to have most low-level wizard walking around with a battery strapped to their back.

I'd also prefer this society to not be totalitarian.
Because of the context, I already have troubles keeping the government from controlling too many aspects of its citizens lives. It's already in charge of the maintenance of city-sized atmospheres and manages the terraforming process. Here the worst-case scenario would be the government forcing people to charge batteries.

So here are a few possible ways I found to organize the battery market :

1. Batteries are cheap
   Empty batteries are so easy to produce, even poor people can afford to buy their own and sell it to whoever they want once full.
   Advantages : Free market, next to no involvement from the government. Most low-level wizards would choose to carry one, since it would be an additional income for very little work.
   Problem : This society lives on a not-fully-terraformed planet, and I'm afraid any kind of good or resource being abundant and cheap would sound weird.

2. People don't own the batteries they're carrying
   Batteries are owned by businesses, rich families, or public institutions. They pay people to charge their batteries.
   Advantages : Sounds maybe a little more realistic than the previous option. Low involvement from the government.
   Problem : This would be an oligopsony (few buyers deciding the prices), leading to lower market prices. This could deter some people (who have an average-paying job, or who would take too much time to charge one battery) to enter the market.

3. The first battery is free
   When they turn sixteen, every citizen gets a free empty battery from the government, and when they sell a charged battery, buyers are required to give them an empty one, in addition of the payment. Like for the previous options, people aren't forced to do it, but choose to if they want the additional income.
   Advantage : Resolves the problems of the two previous options.
   Problem : Heavy government involvement (even if it doesn't decide the prices or forces people to wear batteries).

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Question

Knowing all that, how should the magic battery market be regulated?

(Feel free to build from one of my solutions or to give an entirely new one)

Answer 1

No Regulation needed.

The battery comes in two pieces: an extractor component which stays mounted to the host's back and a removable "bottle" which holds the magic. The bottles are just blown glass with a particular glyph carved on them, so they can be manufactured in vast numbers, making them effectively free.

Charities could give bottles away to the poor to allow the recipients to earn a living.
Extractors might come with a special blue bottle which can only be removed by the manufacturer. The new host wears the extractor till that blue bottle is full, then returns to the manufacturer who receives its contents as payment for the device. One blue bottle pays for one extractor and once the blue bottle is removed, other cheap bottles can take its place. From there, the host owns whatever magic is produced.

Answer 2

Another free-market possibility: a mix of commercial and personal battery chargers. Poor people can wear a locked device, which earns them a fraction of the value of the magic when they swap full for empty. As people get a better magical credit rating they get courted by higher-class providers who pay a better rate. (The longer it takes you to charge a device the less desirable you are to the providers, as the return on investment is less.) You can also buy an unlocked device that lets you sell your magic to the highest bidder; once you own your own device it doesn't matter to the buyers how long you spent producing the magic. (There is a parallel with locked and unlocked mobile phones in the US market that might not be obvious to people in countries with a different business model.)

The trick is making it profitable and convenient enough for even weak magic producers to wear a device.

All that assumes that the harvested magic is not useful as-is, but is going to magic refineries. If I want to wear a magic concentrator so I can fly to and from work with my daily magic budget then the financial picture changes significantly; I benefit from wearing a battery even if I never bring magic in to be deposited. In that case the OP's thought of parallel tanks starts to make more sense, where the owner of the device siphons off a certain amount. (Another American analogy comes to mind, sharecroppers who paid rent on their farms with a portion of each harvest. Note, though, that sharecropping is historically associated with an assortment of predatory legal and financial practices.)

A less-abusive way to get into the magic market would be to have all schools fit kids with fully-locked magic collectors, in part to help pay for schools and in part to tamp down on magical student horseplay. Once or twice a week the kids would have "magic class" where they learn how to do common tasks with magic, just like I learned cooking and sewing and B/W photography in junior high school. That would help spread the social idea that everyone wears a collector to not "waste" magic.