Magic Crystals

Someone help me with the development of this mechanic I am trying to incorporate into a homebrew.

Technological Advancements

Around the time that warforged were created, a gnome named Whizzle Torbang, discovered these crystals in the Far Mountains. After extensive study, he named these Magic Crystals. He found a way to use these crystals to power things such warforged weapons, electronic technology, and other things like that. These crystals are extremely rare and expensive and require a high powered arcane magic user to operate.

Rules for Magic Crystals -
To activate a Magic Crystal it requires a spell slot of 3 or higher. The higher the spell slot, the longer the crystal will last. Imbuing a crystal with another spell slot while currently powered will not extend the life of the crystal.
Level 3 = 12 hours
Level 4 = 18 hours
Level 5 = 24 hours
Level 6 = 36 hours
Level 7 = 48 hours
Level 8 = 72 hours
Level 9 = 96 hours

Thoughts...
This must be for a D&D Game. ?
How do you plan on players using there? How do you want the plot to interact with them? How do you want the players to find out how to use them? Is there a limited number of these? Is there a way to make them(currently)? Can they be recharged?

D&D 5e.

Players can use them a variety of ways. Powering vehicles, airships, certain weapons.
Players would have to learn from someone that knows how to use them, particularly certain artificers.
There are a limited number, but more are always being mined and refined.
You cannot make them, only refine the raw crystal.
You can recharge them whenever they run out by using a spell slot.

I think you may make a counter for them so that (for example without thinking about number balance)
A 3rd level spell slot would give 20 energy. A medium machine takes 2 energy /hour just to run, and if it has a weapon (or special ability) that takes an energy or two...
So a small machine could take 1energy/hour and a giant machine could take 4 /hour...
then you could do things like a blimp (slow) takes 4/hour but something faster could take 6/hour etc etc

I like PhoenixScientist's idea. It stands to reason that a "magic flashlight" will not take as much energy (or charges) out of a crystal than a "magic train" would...

That is an interesting idea.

How does this design balance differently than mine? (If at all, i.e. how does this design improve on mine). Not trying to be rude or pedantic, just curious.

I guess I didn't specify in the OP. Different items would also require different sized crystals, so a flashlight would need a smaller crystal that puts out less power in the time, whereas a train would need a larger one and possibly multiple.

Some sort of sliding scale like you did earlier would work well. Whether you simply want to change the term "hour" for "charge" or come up with entirely new values is up to you.

Like I don't know, let's say I extrapolate on PhoenixScientist's example above, perhaps it could look like...

Level 3 = 20 charges
Level 4 = 30 charges
Level 5 = 45 charges
Level 6 = 65 charges
Level 7 = 90 charges
Level 8 = 120 charges
Level 9 = 155 charges

Tweak the numbers to fit your needs.

Ok, so that is a bit different. I was saying that the point of the energy charges would be that it wouldn’t be based on time it would be based on the machine and the crystal. This way it itemizes the different effect of using a different spell slot and using a different device. From what I understand of yours it doesn’t matter what device it is in, a 3rd level slot will power a mech and a flashlight for the same time.

Plus maybe have larger crystals be able to take larger spells and put out more charges at a time.
For example a second tier crystal can hold up to a level 6 spell slot and put out 3 charg s at a time (so it can’t power some things that take more to run).

So basically you have something like:

A third level spell grants X amount of spell charges into the crystal.
A Blimp requires X amount of charges to fly for Y amount of hours?

Something like that, yes.

One reason for this is actually the weapon power running on the charges so that each weapon fire feels like it costs something.