BCD396XT: Battery Calibration Issue

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Stevenme

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My 396xt has developed a strange issue with the battery voltage circuit. I recently started using the 396 after it sitting idle in a drawer for several months. I replaced the batteries with a fresh set (just charged) of NiMH 2500ma batteries. After using the 396 for a hour the battery icon started to flash . Thinking the batteries were discharged I tested them with my multimeter. They were still fine at about 1.28v. Putting them back in the 396 I was able to power up and check the voltage by depressing the volume and it read 3.50v. Turning the light on caused the radio to shut off.

Some quick math shows 1.28 * 3 to be 3.84. Knowing that the voltage drops when under load I could see it being less than 3.84 when the 396 is on, but not at the point of low battery shut off. In the past I was usually able to use the batteries until they were about 1.2v. My thought it that somehow the battery calibration is messed up, but I don't know how to force it to re-calibrate. With the current threshold where it is I can only get 2-3 hours from just recharged batteries, when I used to get closer to 8 hours.

Has anyone seen an issue like this? I tried a full reset and even reflashing the firmware, but the problem persists.
 

wtp

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just because it is new

doesn't mean it works.
you might have one cell that is bad so the radio dies.
you could check current with a bulb from a flashlight
if it lights up pretty good it is ok, you will see soon how bright it should be
many here like the maha 9000 to recharge batteries externally and it will give you the real mah of the battery
cheap recharge units figure that the battery is at minimum voltage and will charge the for 14 hours no matter what. the smart ones will stop when full.
 

UPMan

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Even "dead" batteries will show good voltage when not under load. Not saying that there isn't anything wrong w/the scanner, but your test methodology does not rule out a bad cell, either.
 

copperhd

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Try new batteries first, even if you just have alkaline. NIMH's will/do wear out/go bad.
 

Stevenme

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All good points, thanks. I've tried several sets of know good NiMH batteries and they all behave the same way. I use them in different devices including flashlights and they perform great. I tested again last night using my best PowerEx set and managed 3 hours before the battery icon was displayed. When I checked them with the meter they were still at 1.26v.

One interesting observation is that with the 396's Power Save Off, held on a single channel with no audio, the voltage meter on the 396 bounces around +/.02v. I don't every remember noticing this before.

I have a great 8 cell Maha charger but it doesn't have a current readout. I'll have to pick one up to be 100% sure the power source is fine. I'm also going to try back reving the firmware to 1.10 just to see if I have some kind of conflict. If I remember correctly, I was one of the early adopters of the 396XT (coming from a 396T) and I wonder if I have an old hardware rev that doesn't work well with the latest firmware.
 

Stevenme

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It turns out that the 396XT was spot on and it was in fact my most trusted Powerex/Duracell batteries. Having worked with rechargeables for 20 years I thought I could spot a bad cell but this one threw me a curveball.

According to my new MH-C9000 (best $50 I've spent in awhile!) not one, but two of the three cells didn't pass the the initialization test. My other Maha charger didn't complain and would charge them but apparently the cell was damaged and didn't provide the amperage needed. I guess what really threw me off the trail was that another set of Duracell NiMH I used had exactly the same issue as the Powerex, one good cell and two failing cells. Independently all 6 cells worked fine in a flashlight test which added to the mystery.

The real test is voltage under load which is what the 9000 does to detect failing cells. Thanks for all the advice and I can't believe that even for a moment I thought the 396XT could be at fault!
 

copperhd

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I suspected you'd find a dead cell from the start, but it could have been worse. I've had new cells go bad just from lack of use just sitting around in a flashlight after the first initial charge from lack of exercise, so now I only keep what I currently use + some in the charger to swap out. Glad it wasn't your 396.
 

wtp

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nickname

my nickname for my 396t is "$500 battery checker".
just fyi if they are charged the batteries should be about 4.00 to 4.25 volts.
 
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