When a buyer is concerned about the charging speed of the UMS4 charger.
The same approach applies to the UMS2, SC4, and other Nitecore chargers, but the specifications differ.
1) Check the specification to see if it's within the range
Output Current QC Mode 3,000mA*1 (MAX) 2,000mA*2 (MAX) 1,000mA*4 (MAX)
Output Current Standard Mode 2,000mA*1 (MAX) 1,000mA*2 (MAX) 500mA*4 (MAX)
2) Why does it take longer to charge the battery when it's almost full?
What you’re seeing with the UMS4 is normal, and it’s likely not a malfunction.
The UMS4 uses a smart charging algorithm. Unlike basic chargers that simply push a fixed charge current, the UMS4 continuously monitors voltage and battery condition, then slows the charge rate as the batteries approach full capacity to help protect battery life and prevent overcharging.
If the charging slows down when your batteries appear to be in the final top-off stage, the UMS4 charger is doing what it’s designed to do.