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Old 10-11-03, 03:50 PM   #1
AquariaGuy
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Question about batteries and the chargers. Please help me!

well i recently bought 4 AAA batteries from BestBuy at 750 mAh at 1.2 V. I'm using it for a small digital camera. Now, i bought a charger at Radio Shack, but i'm not sure how long it'll take to charge them. I'm trying to figure out the math. It says the timer on the charger is 2.5hrs, so i'm assuming after 2.5 hrs, it'll automatically turn off. Input voltage range: 11VDC to 16VDC Charging Current: AA: 1000mA AAA: 400mA. That is the part i don't understand. If it says the "typical" charge on it is 400mA, how long will it take to charge a 750mAh? If it's longer than 2.5hrs than the charge is basically useless, if it doesn't charge it to the max, because it'll ruin the battery. I saw a overnight charger, but it said it would take 13 hrs to charge this 750 current battery. So i thought i'd just get the quick charger. But now that i opened it, i'm not too sure if it'll actually charge the battery to the fullest. Please help. Thanks!!

Matt
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Old 10-11-03, 07:35 PM   #2
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I don't have an answer to your question, but here's what I do: when I'm not using the camera, I put the batteries in the charger automatically, and when I'm ready to use them, I take them out and put them in my camera and use them. Then when I finish, I pop them back in the recharger. My batteries are always at the max as long as I do that.

Could you recharge 8 batteries so that if you're using the 4 AAA for your camera, you've always got 4 on reserve and ready to go? I do that too, and it works well for me. I never worry about if I need batteries or if they're going to last.

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Old 10-11-03, 08:01 PM   #3
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Are we talking NiMH batteries? Charging time is pretty arbitrary. The general rule of thumb is charge until the battery gets warm... pretty scientific eh? At 2.5 hrs delivering 400mA, simple math tells you that you're pumping 1000mAh. Of course the battery won't accept all that. I would advise limiting your charging time to 2 hrs.

That said, you really want to avoid deep-discharging your batteries on a continual basis. This will ruin the battery. Periodic cycling for NiCad and NiMH of course is advisable but you don't want to do it all the time. And when cycling, you want to trickle charge them to avoid gas venting. Trickle charging is generally done at 10% capacity. Figure that on average, you should drop down to about 5%-10% of the battery charge before recharging them. Drawing power when you're at much lower is risking cell reversal. I guess my point is that since you will rarely be starting with zero charge, you should be fine with a 2.5hrs charger delivering 400mA.
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Old 10-11-03, 10:31 PM   #4
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Well the batteries are not purposely for a main camera, it's just a web camera/ digital camera combo.. my real camera has Canon Lithium Ion. Those things are the greatest!!

khuon: i think i worded my question wrong, my battery is 750 mAh, or maybe i'm just confused. ok, you said 400mAh so that means 1000mAh in 2.5 hrs. so if my battery is 750 mAh it'll take about 1.8 hrs. (not being exact) Is my thinking right?

I thought since the battery charger meant 400mAh, that, that was for 2.5 hrs in total. like the max/avg. current it can pump up before the timer turns out.

I think i know what you mean now, i just understood it tottally wrong.
Thanks
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Old 10-12-03, 10:52 AM   #5
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I have NiMH batteries and a charger. The advertised charging cycle is five hours. I can mix and match, one AAA, one AA and one C and a D, or any combination.

If you are using NiCads, they have memory. If you pop them in the charger when they are not fully discharged, they will never reach a full charge. They will charge to where they are at, being 50% or 10% or wherever.

As to your specific problem, Radio Shack people are supposed to be knowledgable. Go back to the store and ask. If the salesperson can't help, ask to see the manager. If he can't help, he should give you a customer service number. I used to be a part time Radio Shack employee and that is the way my store operated.
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Old 10-12-03, 04:02 PM   #6
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Quote:
Originally Posted by TrekRider
I have NiMH batteries and a charger. The advertised charging cycle is five hours. I can mix and match, one AAA, one AA and one C and a D, or any combination.

If you are using NiCads, they have memory.
Both NiMH and NiCad have memory. NiCad memory is much worse however. You should fully cycle both types of batteries periodically but doing so also shortens their lifespan so you don't want to do it all the time. You also want to trickle charge back from a deep discharge.
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Old 10-13-03, 06:16 AM   #7
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Quote:
Originally Posted by khuon
Both NiMH and NiCad have memory. NiCad memory is much worse however. You should fully cycle both types of batteries periodically but doing so also shortens their lifespan so you don't want to do it all the time. You also want to trickle charge back from a deep discharge.
I am not sure that NiMH batteries have memory. My daughter has them in her calculator. She used it doing her homework and studying for a mid-term Calculus exam. She used the same calculater in the mid-term, and the darn batteries couldn't remember one answer!

Must have been defective?
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Old 10-13-03, 09:19 AM   #8
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Quote:
Originally Posted by AquariaGuy
my battery is 750 mAh, or maybe i'm just confused. ok, you said 400mAh so that means 1000mAh in 2.5 hrs. so if my battery is 750 mAh it'll take about 1.8 hrs. (not being exact) Is my thinking right?
Yes. In fact, you're be better to take the batteries off the charger after the 1.8 hours rather than leaving them for the full 2.5 hour cycle. At such a high charge rate you'll be overcharging the batteries which will do more damage to them more rapdily than any memory effect ever will.

On the memory effect thing, with NiMH batteries everything I've read indicates that for prolonging battery life, and for getting the maximum run time, you should completely discharge the batteries every time before charging. This is different to 'deep discharging'. A discharged battery won't run your camera, but will have some residual charge remaining. A deep discharge means absoloutely no charge is left in the battery at all. Repeatedly topping up either NiCad or NiMH batteries is not advised.
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Old 09-04-06, 12:03 PM   #9
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