NiMH Battery Re-Charging

Hello,
Just got a new handheld radio scanner, and am using rechargeable NiMH batteries in it (four AA).
The manual, and the Forums for the radio, really don't provide a decent
explanation for the re-charging techniques in the radio. I can of course use an external re-charger, but would like to use the radio's built in one, for now.
Questions:
The radio apparently just recharges for a specific number of hours, which is adjustable. The default is 16 hours. It says that it charges at a current rate of 150 mA.
But everytime you turn the radio on and off and then back on again, the timer resets to 16 hours.
So, it seems very easy to overcharge the batteries.
Any potential problems if the batteries already have a full, or nearly full charge, and the radio resets and wants to keep charging them (again) for another 16 hours ?
Sure seems like a poor way of doing it; I would have thought that they would monitor the voltage of the battery directly, and not use this kind of scheme. Probably a bit cheaper, though in circuitry.
Any potential over charging problem ? Caveats ?
Thoughts on ?
Thanks, Bob
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Robert11 wrote:

You'll get less than optimum life from the batteries, but so what?
It is probably a "non-issue". 16 hour charging is not the best approach, but it is not horrible, either. It's actually a pretty good compromise. Eventually, your batteries will fail due to age, overcharging, undercharging, whatever. You can put time, energy and money into getting the absolute maximum life from them, or accept the fact that less than optimum charging and use will give you less than optimum life. In most cases, the delta between optimum life and a somewhat shortened life is not worth the cost and effort needed to get the optimum.
We don't know the specifics of the radio's charger, but as long as you charge using it you are "stuck" with whatever it does. You can manage the situation to some extent, if you wish. If you are concerned about "10 minute per day" (or whatever) operation, you can use the radio that way, and estimate how many days to wait between charges. Or you can pull the batteries out of the radio and charge them with an external charger that has the features you want.
Ed
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Hi Ed,
Thanks for reply.
Any potential danger like overheating, fire, etc. if "overcharged" for many hours ?
Thanks again, Bob
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Not at 150 mA. The batteries are likely rated at 1500 mAh or more, probably above 2000 mAh if they were purchased recently. So you're charging them at what is called the C/10 rate or even less. The cells can withstand that charge rate indefinitely, only getting a little warm if they are already fully charged.
This will reduce their life compared to a good fast charger, but NiMH cells aren't that expensive to replace when they eventually fail.
    Dave
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Always possible.
My advice would be a proper external charger - one of the "clever" ones.
I have one here, it charges only until the cell is fully charged. It has four channels, to allow four cells to be charged simultaneously, each monitored independently. Each channel has an LED. When the LED goes out the cell is charged. It is not unusual, even with a set of four always used together to see the LEDs go out a different times.
--
Stuart Winsor

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Robert11 wrote:

No. Provided the charger in the radio doesn't become defective and is used per directions, you could leave the batteries charging in there for years and not have a fire. The batteries might be ruined by that, but that's the extent of the likely problem.
Ed
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