BC125AT Charging issues

[scanman1958]

After owning a new 125 for about two weeks I decided to see what kind of charging rates and/or drain the unit has while plugged in to a power source. This was a very basic test but it ended up pointing out to me a potential problem with either the scanner's charging circuit or the batteries. Here it goes.

The start of the test was using a cigarette lighter adapter for the USB chord and the screen light was "off". Was in the SCAN mode and receiving signals. Power level in upper right corner indicated 3.95. After about 20 minutes of scanning the power level was 3.90. The unit was actually discharging while in use.

Changed to the HOLD mode (monitor only one channel). After about 15 minutes the power level went from 3.90 to 3.87 with the USB chord still plugged in. Still discharging while in use.

Went home and plugged USB chord into a USB wall adapter and charged the scanner over night. Approximately 10hrs. Screen said CHARGE COMPLETE . Turned unit on and the power level was 3.90. (Less than what I started with the day before.) Then I turned scanner off. About three hours later turned scanner on. Power level stated 3.85. Unit seems to be draining the batteries even when off.

Plugged unit back into the cigarette lighter adapter but after about 15 minutes noticed the back of the battery compartment warm to the touch. Unplugged everything. Took batteries out. Double checked the battery setting. It is set to NiMH. Put batteries back in and plugged USB charger back in. After about five minutes screen said BATTERY ERROR.

Unplugged charger and checked power level. Screen said 3.90. Turned scanner off. About 30 minutes later checked power level again. Now it was 3.67. Batteries discharging at a faster rate now when scanner is off.

Thought I had one bad battery. Checked battery level on meter. One was 1.25v the other was 1.27v.

I am at a loss and am asking for advice. Back to Uniden for repair or try new batteries? I am using the batteries that came in the box.

 

[UPMan]

1) You cannot determine the charge state by checking voltage. The terminal voltage is going to depend on many factors, including the instantaneous load being drawn by the connected circuit.

2) It is normal for the battery terminal voltage to drop after charging is complete. Charge voltage is at a higher level than rated terminal voltage (which is ~1.25 V/cell). With no load, it takes some time for the battery terminal voltage to drop.

3) Except in the case of a completely shorted cell, you cannot determine the condition of a battery by checking its terminal voltage. A completely discharged battery, removed from a load, will still measure around 1.25V.

4) It is normal for NiMH batteries to get warm during charging, even when not in over-charge condition. Unlike NiCd batteries, which are endothermic during charge and only get hot during an overcharge condition, the chemical process involved in charging NiMH batteries is exothermic.

5) The BATTERY ERROR message can indicate a bad cell. If the battery terminal voltage behaves abnormally (rises too fast, doesn't rise at all, etc) during the first few minutes of charge, the scanner detects this as an error state and stops the charge cycle. This same method prevents charging of alkaline batteries, even if you leave the switch in the NiMH position. If the message recurs, I'd try another set of batteries.

 

[scanman1958]

Thank you Paul for your informative reply. Glad it wasn't a shrug of the shoulder response. Let me respond to your reply as best I can.


1. I know you need special tools to check proper voltage, load and drain etc. But I don't have those and I was using what I had to check what I thought was wrong.

2. Some people may see voltage drop after charging but I have not. Especially the drastic drop I was seeing on the 125.

3. Again I was using what I had and was hoping to find that "obvious" bad battery. That's all.

4. I have not noticed a warming of batteries in any of my other battery operated scanners. It may happen but I have not noticed over the years.

5. I did try another set of batteries. I actually grabbed a couple that I have as a reserve set. They are name brand batteries and about a year and a half old and had been used a lot. They are working nearly perfect so far.

With the new (old) batteries I have no battery drain at all. Not in SCAN, HOLD, light on, light off or even when the scanner is off. With the "in the box" set of batteries, they were draining even when plugged into a power source. The scanner has been off for over two hours and the battery level is the same.

I am suspecting a bad batch of batteries from Uniden's supplier. (it can happen)

Thanks again Paul.