That charger will be fine with the emag battery pack. It is designed to charge large capacity packs with voltages from 12V to 16.8V. It just doesn't trickle charge, so you can't put the charger on to maintain a full battery pack. It is a high capacity all or nothing fast charger.
The emag batter pack is a high drain pack.
The 16.8V rating on a battery pack is the average voltage. When the pack is fully charged the voltage output is above 16.8V and when the pack is empty it is below 16.8V.
Except for the Automag in front, its usually the man behind the equipment that counts.