Rather than totally rework someone else's suggestions, here's mine:

Preface:

Drain mines are worthless as currently configured. It's not enough to momentarily drain a cell, drain effect must be sustained.
Drain technology is promising but not very well implemented.
Mines have limited use in game.
Even when batteries are completely drained, strafe maneuvering is still possible.

Proposal:

-Modify drain effect to last 2 seconds at 500 charge / second (so that all commonly used non-capital ship powercells are completely drained for 2 seconds).
-Add concussive force to mine (so that ships will be inhibited from maneuvering normally)
-Reduce damage to 1 (damage not the point of these weapons)
-increase mass to account for additional technology
-increase splash (EMP and Conc radius should be the same, and wider)

Drain Mine (new stats)

Port: large
Damage: 1
Delay: 2s
Mass: 2000kg
Splash: 200m
Proximity: 70m
Ammo: 10
Cost: 6x current price

I like where you are going with this. Maybe 5 second life at 200 charge per second and 300m splash.