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huisjen
08-08-2009, 05:09 PM
Somewhere I heard that if you have a rechargeable battery such as a ni-cad or lithium ion, and it develops a charge memory, that you can erase this by giving it 3x the charge voltage for about ten seconds.

Has anyone tried this? My cell phone battery needs a dope slap.

Dan

paladin
08-08-2009, 07:28 PM
Dan...batteries haven't had memory set for years. Batteries naturally deteriorate over time and accept less charge. Maybe time for new cells.

LeeG
08-08-2009, 08:17 PM
Nicad have memory,not lithium ion or NiMh. Your phone is post NiCad. Lithium Ion will degrade with high temps. If you have a fully charged lithium and put it on the dash of your car and it heats up to 140degrees you're aging your cell in rapid time. Same with lap top. Imagine your battery is a piece of cheese., don't put it in hot places when fully charged.

brad9798
08-08-2009, 08:26 PM
My 18V tool batteries had that problem ... here's what I did:

Took a battery charger with two pieces of insulated 14 gauge wire.

Attached one wire to the negative of the charger and to a prong of the battery.

Attached the other wire to the positive of the charger and then took the other end and touched it to the 'other' prong on the 18V batteries ...

They hold a better charge again. Not like new, but better.

:)

Brad

Gonzalo
08-08-2009, 09:34 PM
Rechargeable batteries are often left in constant charge mode, so you can just pick up the tool or whatever out of a cradle and use it whenever you want. Usually the battery is only slightly discharged when you put it back on charge. When left in this mode, ni-cads will develop an increase in internal resistance when only partially discharged.

Say you only use 10% of the battery's charge and then put it back in the cradle until the next time you use it. After a few cycles of this, the internal resistance will increase from about the 10% discharge point until you have used all the available charge, as defined by the open circuit voltage. If you try to discharge the battery past the 10% point, the additional internal resistance will reduce the current delivered, so your drill or whatever will turn slower and you will think the battery is nearing its discharge point because of the memory effect. There is still a lot of charge in the battery, but it is only available at this lower current.

This is the way manufacturers explain memory effect in internal publications. I have several times run tests on ni-cad batteries, and this is a pretty fair description of what happens. However most manufacturers deny publicly that any memory effect exists.

Supposedly if you completely discharge the batteries, this effect can be eliminated. In the tests I have run on ni-cad batteries, this hasn't ever really worked. However, the deep discharge seems to damage the batteries and reduce their life.

In my experience the best way to get long life out of a ni-cad battery is to leave it on no more than a constant .1C charge (100 ma for a 1000 ma-hr battery, about a 16 hour charge rate) and just use it a little bit before putting it back on charge. I've had some that I've operated this way for more than 15 years, and they still work ok.

Charge it much faster than that or discharge it deeply very many times, and the battery life is shortened.

I wouldn't believe what manufacturers say about no memory effect for nimh batteries, either.

Gonzalo
08-08-2009, 09:43 PM
Leaving any rechargable battery on a constant high rate of charge (above .1C) seems to shorten their life, also. If you have a laptop with an nimh battery, the best way to get long life is to turn it off when you are not using it and disconnect the power cable as soon as the battery is charged up. If you leave it connected to the charger whether it is running or not, this will shorten the battery's life.

Some people go so far as to remove the battery from the laptop when it is in use plugged in, so none of the operating current goes though the battery. You put the battery back in only when you are using it on battery power, and charge it only as long as needed. This is too much trouble for me, because I like to have my laptop available without having to crank it up every time, but I pay for it with shorter battery life.

Some devices have "smart chargers" that can sense when the battery is fully charged, and then shut off the charging current, but none of my laptops do.

I don't know whether any of the above applies to lithium cells.

LeeG
08-09-2009, 12:03 AM
you cell phone battery is probably lithium ion, google lithium ion and battery care.

brad9798
08-09-2009, 07:26 AM
... and eventually, batteries DO need to be replaced!

And Batteries Plus, the West Marine of batteries, is there to WAY overcharge you to replace it ... but they do stock just about everything you might need.

:D

LeeG
08-09-2009, 12:19 PM
me thinks lithium Ion battery chargers have a particular charging rate profile and aren't a straight constant voltage charger. If you blast a high current through it you might have fireworks, not sure. Even though the benefit of lithium ion is a high charge rate I don't think a bum lithium will benefit by uncontrolled high current if the battery is simply near the end of it's life. I don't think the characteristic Norman is talking about applies to lithium ion.