You may have a standard wall charger, which is not recommended usually because it won't stop charging the battery when its full. That could cause overheating, and potentially ruin the battery.
However, most wall chargers do have a description of its output on the adaptor itself, which is crucial in calculating how long you must charge it.
For example, the output may read "DC 9.6V 500mA". Using this, combined with your battery's capacity of 1600mAh, you can calculate the charge time.
1600mah/500mA = 3.2 hours.
In this situation, you would need to charge the battery for 3.2 hours from
completely empty to full. If the battery still has some juice left in it, you run the risk of overcharging.
This is why smart chargers are recommended, since you can never be certain how much juice is left, and how to adjust your charge time.