With Mining Gadgets 1.11.0 and Charging Gadgets 1.7.0, using a Modification Station to add or remove a Battery Upgrade on a Mining Gadget will charge its internal energy storage by 1 FE every time.

To reproduce:

1. Install the aforementioned mods or the Direwolf20 1.18 mod pack.
2. Get a Modification Station and a energy-depleted Mining Gadget.
3. Get a Battery Upgrade. It does not matter the tier.
4. Add the Battery Upgrade to the Mining Gadget.
5. Notice it has been charged by 1 FE.
6. Remove the Battery Upgrade from the Mining Gadget.
7. Notice it has been charged by 1 FE.

This could be used to very slowly charge the gadget so a player can mine a block for free, but this is very slow (less than 100 milliFE/t at best)

Please re-open if this is an issue still in 1.21

Looks like this was always and still is an issue.

You're still sending 1 FE to the Mining Gadget when its max energy updates, here:

This is also present in 1.20.4 and earlier versions:

And since at least 1.15: