Free wall chargers and free batteries that comes with free with your AEG are for "just to work / testing" purpose. They are low power, low mAh and free.
We recommend getting something better.
A Good 8.4V or 9.6V Battery is recommended for AEG to perform smoothly.

*Smart Charger recommended for good batteries. If you don't have one yet, invest in one today. It will enhance battery life / performance and ultimately safe you money.
Smart Chargers "times", "Charges better", "Charges faster" and "stops charging" for you.

All Airsoft guns use a 8.4V or 9.6V battery (200~400 fps). The stronger your spring (the higher the fps), the higher (V) and (mAh) you need on the battery.
Wall chargers charges 200~300 amp into your battery pack per hour. And it will keep charging until you unplug it or battery dies.