Why does a twin charger only charge one battery at a time?

Why does a twin charger only charge one battery at a time? trimble dual slot battery charger manual Product Note: Dual slot battery charger with power supply and cord for Trimble GNSS receiver batteries Loading Quantity trimble charger dual battery slot Unplug the charger from the wall, then the battery receptacle 2 COLOR LEDs FOR STATUS INDICATION A POWER LED : • Red color -Power on • Green

trimble charger dual battery slot The Dual-Slot Battery Charger with Power Supply for Trimble GNSS Receiver can be used with a Trimble Total Station or MT1000 It comes with two slots and

slot get clucky Case for holding 2 x Dual slot chargers, 4 batteries, 3 battery external holder and associated cables SKU 58386001 This items ships in 14 days $  Charge the battery completely before using it for the first time B Tip