Spark when connecting battery module to DC power supply
The spark is caused by your battery charging the output capacitor on your power supply, which is zero volt when you start and have very low impedance so the current consumption from the battery is huge the monent you make contact, i.e. big spark.
The easiest way to get rid of it is to place a suitable diode in series with the power supply and increase the voltage by 0.7 V to compensate, or 0.4 V if you go with Schottky.
Source: designed battery chargers for a living for six years.