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Old Mar 13, 2007, 11:53 AM   #1
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I have been slow to embrace the rechargeable battery market aside from my new camera (D50) and I have some questions about recharging.

1. Should you fully drain a battery before recharging?

2. What charge level should you store a rechargeable?

3. Do modern rechargeable batteries develope "memories" (ie if you recharge when its at 50% capacity over and over the battery acts dead when it gets to 50% because it is used to being charged at this time)?

4. Do the answers depend on the type of rechargeable?

I remember when rechargeable batteries first came out and they weren't too reliable. Some people made little circuits with a light bulb to fully discharge batteries. When the light went out they knew there was no power left and then recharged them.

Thanks for your help!
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Old Mar 13, 2007, 2:53 PM   #2
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Quote:
1. Should you fully drain a battery before recharging?
No. Doing so only degrades it faster.
Use it normally and recharge it when you can. Every fifteen partial cycles or so, discharge it fully once.

Quote:
2. What charge level should you store a rechargeable?
About 40% for Lithium-ion or Lithium-polymer, irrelevant for NiMH.
If by "store" you mean leave it unused for months, that is. If you use them often don't bother.

Quote:
3. Do modern rechargeable batteries develope "memories" (ie if you recharge when its at 50% capacity over and over the battery acts dead when it gets to 50% because it is used to being charged at this time)?
No. Some develop voltage depression, though. More on this here.

Quote:
4. Do the answers depend on the type of rechargeable?
Of course.

Quote:
I remember when rechargeable batteries first came out and they weren't too reliable
Heh. The bad old days when the only available rechargeables were NiCD cells... I'm so happy I was too young to care then

Quote:
Some people made little circuits with a light bulb to fully discharge batteries. When the light went out they knew there was no power left and then recharged them.
This is a bad idea. It pays to fully discharge a cell every once in a while, but "full discharge" means getting a cell down to maybe 0.8 volts. A rechargeable that can only output 0.8 volts into any load is dead flat.
Discharging any cell to complete, absolute zero will do varying degrees of damage to it.
Lead acid cells will sulfate and become useless, NiCD ones will probably (but not certainly) shrug it off, NiMH ones can lose some capacity, Lithium-ion ones can die, and if you do it to a Lithium-polymer cell you'd better have a fire extinguisher handy.
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Old Mar 13, 2007, 4:02 PM   #3
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Violet sky wrote:
Quote:
Quote:
2. What charge level should you store a rechargeable?
About 40% for Lithium-ion or Lithium-polymer, irrelevant for NiMH.
If by "store" you mean leave it unused for months, that is. If you use them often don't bother.
I would tend to disagree with this answer. If you plan to store your batteries for a long time, then I would give them a full charge before mothballing them.

Probably doesn't matter too much for NiMH as they self discharge anyway, but LiIon's tend to hold onto their charge very well.
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Old Mar 13, 2007, 4:28 PM   #4
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Thank you Violet Sky and amazingthailand, your answers have helped a lot. Idefinitely don't want any fires in my camera!I will double check my battery types and treat them accordingly.
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Old Mar 13, 2007, 10:02 PM   #5
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My understanding:

Li-ions:
- long term storage at 40%
- don't run them down til the device shuts off (deep discharge), no discharge cycling required
- don't keep them at 100% and not use them
- no memory effect

NiMh:
- do run them down til the device shuts off occasionally (eg, every 5 cycles or so)
- don't run them down every time however
- storage charge doesn't matter too much, they'll self discharge anyway (except the Eneloops)
- some memory effect, less than Ni-cads, more than Li-ions (hence periodic deep discharges)

Both:
- recharge at least every 6 months, even if stored
- using them is better than not using them
- keep them from hot environments (car in the sun)
- if your device has a true battery "fuel" gauge, then it is supposedly good to deep discharge once/month (even Li-ion) to reset the battery gauge (but it is still not healthy for the Li-ion). if no real gauge, not necessary to deep discharge (to reset fuel gauge, anyway)
- don't fast charge (15min).. causes batt to overheat, reducing life
- buy quality batteries and a quality charger
- read: http://www.batteryuniversity.com/index.htm
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Old Mar 14, 2007, 7:07 AM   #6
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reppans wrote:
Quote:
My understanding:

Li-ions:
- long term storage at 40%
- don't keep them at 100% and not use them
In everything I have read, I have never heard this. Do you have a reference? There can be a big difference between understanding and fact.

In fact for well over 15 years, I have been storing my LiIons with a full charge and I have never had a problem.

The ONLY problem I have ever had with a LiIon battery was when I left one attached to a camcorder for too long a period of time. When I went to recharge that battery it was D E A D. Voltage reading was 0 volts. Nothing I did could revive it. Lesson learned.
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Old Mar 14, 2007, 7:10 AM   #7
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Violet Sky,

I finally had the chance to read the link you posted. The author was right about the radio controll enthusiasts, thats where I saw the light bulb dischargers. Though they did not discharge cell by cell so they ran the risk of reverse charging.

reppans,

Thank you for information and the link to the Battery University! I will have to spend some more time reading all the papers but there is really a wealth of knowledge in there.

TwoStep
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Old Mar 14, 2007, 11:08 PM   #8
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amazingthailand wrote:
Quote:
reppans wrote:
Quote:
My understanding:

Li-ions:
- long term storage at 40%
- don't keep them at 100% and not use them
In everything I have read, I have never heard this. Do you have a reference? There can be a big difference between understanding and fact.
http://www.batteryuniversity.com/parttwo-34.htm

http://en.wikipedia.org/wiki/Lithium...n_battery_life

there are others, but batt university seems to be the acknowledged expert site on the subject.
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Old Mar 15, 2007, 7:19 AM   #9
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Interesting stuff. Live and learn. Guess I'll store my LiIon's in the fridge from now on.
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Old Mar 15, 2007, 10:27 AM   #10
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As far as NiMH go, the new hybrids like the Sanyo Eneloop and Ross Hybrio cells definitely rule. They may only have a capacity of ~2000mAh but they sure do hold a charge for a good long time when not used. The newest hi-capacity 2700-2800mAh cells will run the same camera longer if they have just come off of the charger but most people tend to charge their batteries, put them in the camera, take some pictures and then put the camera away. The next time you go to use the camera the batteries are already half dead - not so with Eneloop or Hybrio cells which hold up to 85% of their charge for months.

Being that it's winter in many parts of the countrynow it is important to note that all NiMH cells will suffer in cold weather, often losing up to 50% of their capacity when the temp is freezing or below. Lithium batteries fare much better in the cold but there are no AA size rechargeable Li-ion batteries, only the one-use type.
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