User blog comment:Godisme/Gray vs. Doriate/@comment-3424593-20130906210035/@comment-7418318-20130906212633

So far there was never the combination of both the availability of such a power source and at the same time the necessity to use it. In other words whenever a mage had insufficient magic power, there was no such external magic power source available and that's why the exact same method wasn't used before, but even so similar things have already been done in the series so far:

Azuma did something similar by "hacking" into the magic present within Tenroujima and using it against the Fairy Tail mages.

The way that all magic in Edolas worked was pretty much the same thing (suck magic either from natural deposits or other beings and use it in some other way, like powering the magical items)

The Eclipse Gate was charged by using a similar principle, only they stored the energy, rather than immediately discharging it again.