I am not familiar with the BC125 (UBC125) but with other Uniden scanners that take either alkaline or rechargeable batteries, two things.
There should be a switch in the battery compartment labeled Alkaline or Nicad. In the Alkaline position, you cannot charge any battery, it's a safety thing so you don't try to recharge alkaline batteries.
So, depending on what kind of batteries you put in, and the state of those batteries' charge...
If you are using alkaline batteries NO, do not try to charge them! Make sure switch is in alkaline position!
If you are using Nicad or NiMh batteries, yes, you may have to charge them. Make sure the switch is in the Nicad (NiMh) position and charge for a while.
Do NOT try to recharge Lithium batteries in the scanner. Use an external charger only.
Hope the above helps.