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Should batteries be run down all the way?

Message #1 - Posted 2003/11/03 - Hobo

I have read a lot of contradictory info on whether laptop batteries should be run down all the way before recharging in order to enhance battery life. Is this true or not?

Message #2 - Posted 2003/11/03 - Phil Stripling

Hobo <noemail@noemail.com> writes:

I have read a lot of contradictory info on whether laptop batteries should be run down all the way before recharging in order to enhance battery life. Is this true or not?

The rumor with NiCads was that if you did not fully discharge them, they would take a partial charge. Then if you _did_ fully discharge them, they would "remember" the last charge and take only that much; i.e., they would not fully recharge the next time. NiMHs and Li Ions are claimed not to have this "memory" problem. See
http://www.alltekpower.com/faq/index.asp?a=6 for several FAQ lists from a seller of NiMHs, taking into account that it is a seller of NiMHs.

Philip Stripling | email to the replyto address is presumed Legal Assistance on the Web | spam and read later. email to philip@ http://www.PhilipStripling.com/ | my domain is read daily.

Message #3 - Posted 2003/11/04 - Gregory Weston

Previously, Phil Stripling wrote:

Hobo <noemail@noemail.com> writes:

I have read a lot of contradictory info on whether laptop batteries should be run down all the way before recharging in order to enhance battery life. Is this true or not?

The rumor with NiCads was that if you did not fully discharge them, they would take a partial charge. Then if you _did_ fully discharge them, they would "remember" the last charge and take only that much; i.e., they would not fully recharge the next time. NiMHs and Li Ions are claimed not to have this "memory" problem. See
http://www.alltekpower.com/faq/index.asp?a=6 for several FAQ lists from a seller of NiMHs, taking into account that it is a seller of NiMHs.

On the other hand, Apple recommends that you run it down periodically (a couple of times a year) to recalibrate the OS's time estimates.

Message #4 - Posted 2003/11/04 - David C.

Phil Stripling <phil_stripling@cieux.zzn.com> writes:

The rumor with NiCads was that if you did not fully discharge them, they would take a partial charge. Then if you _did_ fully discharge them, they would "remember" the last charge and take only that much;

No rumor. The "memory effect" of NiCd batteries is a well established fact. They last longer if you let them drain completely before charging, and let them charge completely before putting them back into service.

Although I don't have a laptop, I have personal experience with NiCd batteries from other devices. For instance, the battery pack on my cordless phone lasts about 5 years before it can no longer hold a full day's worth of charge.

Friends of mine with the same model phone leave the unit on the charger whenever it's not in use. Their battery packs last less than a year.

i.e., they would not fully recharge the next time. NiMHs and Li Ions are claimed not to have this "memory" problem.

NiMH doesn't have a memory effect. Again, this is confirmed through personal experience (using NiMH AA batteries in my digital camera.)

I always used to think that Li-ion didn't, but recently some people have been telling me otherwise, so I'm no longer certain of this. I do know that old laptop batteries can't hold as much of a charge as new ones, but I don't know if this is due to a memory effect or simply to the pack getting old.

-- David

Message #5 - Posted 2003/11/04 - Kirk Strauser

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At 2003-11-04T03:22:19Z, shamino@techie.com (David C.) writes:

No rumor. The "memory effect" of NiCd batteries is a well established fact.

No. At best, it is a well accepted hypothesis that may or may not be true, depending on how strictly you define certain terms. For more info see:

http://www.repairfaq.org/ELE/F_NiCd_Memory.html

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Kirk Strauser
The Strauser Group
Open. Solutions. Simple.
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Message #6 - Posted 2003/11/04 - David C.

Kirk Strauser writes:

David C. writes:

No rumor. The "memory effect" of NiCd batteries is a well established fact.

No. At best, it is a well accepted hypothesis that may or may not be true, depending on how strictly you define certain terms. For more info see:

http://www.repairfaq.org/ELE/F_NiCd_Memory.html

Excuse me. Same symptom, different cause at the molecular level. I'm sure those of us using the batteries can't tell the difference.

His wonderful solution of "never overcharge them" is wonderful if you've got a lab full of equipment to make this possible. Unless he's got a solution that us mere mortals can use, the entire article is useless, even if it's right.

-- David

Message #7 - Posted 2003/11/07 - lewis

shamino@techie.com (David C.) writes in a previous article dated Tue, 04 Nov 2003 03:22:19 GMT:

Phil Stripling <phil_stripling@cieux.zzn.com> writes:

The rumor with NiCads was that if you did not fully discharge them, they would take a partial charge. Then if you _did_ fully discharge them, they would "remember" the last charge and take only that much;

No rumor. The "memory effect" of NiCd batteries is a well established fact. They last longer if you let them drain completely before charging, and let them charge completely before putting them back into service.

Actually it was in the early 1990s when they started making NiCads with actual memory. I remember Popular Mechanics gave somebody an award for that in 1992. The control unit monitors current flow in and out, and it's programmed not to overcharge the battery. But the only way it can compensate for internal leakage is when the battery drains completely, the unit knows that whatever charge it thought was in there must have leaked across so it zeroes it out.

Although I don't have a laptop, I have personal experience with NiCd batteries from other devices. For instance, the battery pack on my cordless phone lasts about 5 years before it can no longer hold a full day's worth of charge.

Friends of mine with the same model phone leave the unit on the charger whenever it's not in use. Their battery packs last less than a year.

Hopefully the control unit in an Apple laptop battery is a little more sophisticated than the one in a $12 cordless phone.

I always used to think that Li-ion didn't, but recently some people have been telling me otherwise, so I'm no longer certain of this. I do know that old laptop batteries can't hold as much of a charge as new ones, but I don't know if this is due to a memory effect or simply to the pack getting old.

Battery packs wear out no matter what you do.

-- spud_demon -at- thundermaker.net
The above may not (yet) represent the opinions of my employer.

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