The GM Controller have some large capacitors that charges up when power are applied; that's where the spark come from. I'd think most controller has it. After that inital charge/spark, the controller use little power; usually in the 20mA range.
The switch on the GM battery operates on the main power. The GM Magic Controller should also have a 'control' on/off positive wire, which turns the controller on/puts it in standby mode. In standby mode, the controller uses around 2mA, and one avoids the spark alltogether.
I've modified my GM battery pack, and connected main power directly, and connected a third wire via the key-switch to the on/standby control wire.