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Old Oct 8, 2004, 2:09 PM   #1
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I recently bought a Sony Cyber-Shot DSC-P73 camera. It came with two NiMH batteries (specifically NH-AA-DA) specifically made for the camera.

Many places on the internet say such batteries do not suffer from memory effect. But the camera manual itself says that they can. Which do I believe?

My next question assumes the manual is correct in the above regard.Itsays to use up the batteries before recharging by running the in-camera slide show. This seems to me like unnecessary wear on the camera, particularly the LCD screen. If I must use up the batteries, is it okay for me instead to usethem in adifferent device, say a Discman?
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Old Oct 8, 2004, 6:21 PM   #2
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Well.... I think that most sites mean that you are supposed to be able to top them off without any problems.

However, with brand new NiMH batteries, they typically don't hold a full charge, until they have been charged and discharged a few times.

So, that's probably why the manual wants you to discharge and recharge the ones included first.


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Old Oct 8, 2004, 9:47 PM   #3
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When I first bought a set of rechargeable AA's the manual said that to get the best life out of them, they should be charged fully and then discharged fully for three or four cycyles. I charged them until the charger indicated they were fully charged. Then I put them in a flashlight that takes AA batteries and turned the flashlight on. I left the light on overnight, and in the morning, the light was completely out. I recharged them and repeated the process three times. I have gotten what I consider exceptional life out of these batteries (Duracell 2050 mAh capacity). There was one period of time when I didn't take any pictures for about a month and a half.I did not recharge them before I used the camera. I still got almost 250 shots out of those batteries.
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Old Oct 9, 2004, 3:21 AM   #4
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Here's what I've posted in another Camera forum to answer those questions:

Essentially:
NiCd (Nickel Cadmium) and NiMH (Nickel Metal Hydride) are approximately 1500 cycles
Lithium (Ion and Polymer) are approximately 300 cycles

Furthermore, the reasons for discharging batteries as you've mentioned only really apply to that of the first group (NiCd and NiMH).

NiCd and NiMH both have the memory effect, which everybody by now should be familiar with. By constantly topping-up such chemistries, say from the 50% mark, what results is the battery "remembering" where it has been charged from and therefore, only giving you 50% capacity in the end. The reason for this memory is because dendrites (crystalline structures) form between the positive and negative electrodes during the charging process. By allowing the batteries to run flat, you are slowing (note, I didn't say "preventing") the formation of these crystals and therefore, you experience the battery's nominal capacity for a lot longer.

Of course, whilst NiMH was developed for greater capacity it also had the advantage of a lesser memory-effect resulting in a lower maintenance battery. So consequently, whilst no harm is done, there is no real need to discharge a NiMH every time you need to recharge it - once every 20 recharges or so is just fine. Essentially, think of NiCd as being a high maintenance battery as NiMH being a medium maintenance battery.

When storing NiCd/NiMH batteries, you should discharge them and remove them from your equipment (to avoid any further drain, even though you may THINK the device is off) to prevent the dendrites forming and reaching a point of no-return in the cells.

There are chargers (but purely in the professional/industrial/commercial market) which perform a type of charge called Reflex or Burp charging where during the charge process, there's bursts (or burps) of discharge performed on the battery to help minimise the same issue thereby not requiring you to perform the full discharge like some consumer chargers would be designed with.

HOWEVER, Lithium rechargeable batteries do not have this memory effect. That is, there are no crystalline structures formed within and therefore can be topped up at any time without issue. So the theory of discharging before every charge is in fact more HARMFUL to your battery because you're completing the charge-discharge cycle which means you're one step closer to the 300 mark every time.

So what do you do? Keep topping it up. Whether it's your camera, MD recorder, mobile phone or PDA, just plug it into power for a charge when it's not in use. This way, you avoid the completion of the one charge-discharge cycle and hence you cheat it of its (seemingly) premature death. Not that you will avoid its ultimate death of course, but it will prolong the life of the battery nevertheless.

Forget the electrical engineer side of me speaking here, the proof is in the pudding. I have a 2 year old Nokia 6310 GSM phone which has been using the same battery from my 3.5 year old Nokia 6210 and it is still running at about 75% capacity. That's a 3.5 year old battery that has been topped up almost constantly with only 2 cycles genuinely stripped off its clock when I was gone on a couple occasions and forgot to pack the charger

So there you have it people. I hope this clears up any qualms you have with battery usage.

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Old Oct 9, 2004, 12:56 PM   #5
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Strictly speaking Ni based batteries suffer from voltage depression not memory effect but the therm "memory effect" although a misnomer is accepted. What happens after numerous shallow discharges is that the cell would still deliver it's full capacity but at slightly lower voltage. Since battery meters in most devices measure voltage the low battery sign is displayed sooner with a voltage depressed battery. In practise it is not necessary to discharge fully before each recharge even NiCd batteries, this puts more strain on the cells. With NiMH the effect of voltage depression is less pronounced, so discharging fully once every 15 cycles or so is enough to keep your cells from voltage depression.

Surely you can discharge your cells in any device that takes AA cells. I wouldn't recommend flashlights though. They drain batteries fully. If one of the cells is slightly weaker it may go into reverse polarity and be damaged
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Old Oct 9, 2004, 11:52 PM   #6
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blr wrote:
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Surely you can discharge your cells in any device that takes AA cells. I wouldn't recommend flashlights though. They drain batteries fully. If one of the cells is slightly weaker it may go into reverse polarity and be damaged
I agree, but I wish we could get away from this term 'reverse polarity' for over-discharging of cells. After all, rechargeables are designed to pass current in either direction, i.e., they operate with either polarity within their limits. How much current passes, and in what direction, is determined by the device to which the cells are connected, and by the condition of the other cells in the pack.

What we want to avoid is forced discharge or 'reverse electrolysis' down to less than nothing, which may well damage the chemistry. We mustn't pass current in the wrong direction when the cell's already empty.
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Old Oct 11, 2004, 11:39 AM   #7
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Alan T wrote:
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I agree, but I wish we could get away from this term 'reverse polarity' for over-discharging of cells. After all, rechargeables are designed to pass current in either direction, i.e., they operate with either polarity within their limits. How much current passes, and in what direction, is determined by the device to which the cells are connected, and by the condition of the other cells in the pack.

What we want to avoid is forced discharge or 'reverse electrolysis' down to less than nothing, which may well damage the chemistry. We mustn't pass current in the wrong direction when the cell's already empty.
Agreed, just like the term "memory" reverse polarity is a misnomer, thank you for correcting me Alan T.

I have a charger/analyser that has a program dicharging to 0.8 V/cell and recording the capacity. I run it once every 10-20 shallow cycles in order to prevent voltage depression.
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Old Oct 12, 2004, 3:32 AM   #8
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Yes Alan, I'm sure you are correct about rechargeable's reverse polarity. I've never seen that on rechargeables. BUT many years ago when using a device powered with 2 x AA alkalines, things went wrong. On checking alkalines carefully with the voltmeter, one cell was definately "reversed polarised" Couldn't believe it, and still no wiser today.


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