Tip: Let battery go empty before reloading. Q: Why ?

Question

Hello,The lady at the barber shop said the following:She let the battery of the shaving device go completely empty before reloading it with power. (she had a spare already loaded).She said otherwise it doesn't load properly.I think I am noticing the same effect on my own shaving device.Right now I am completely letting it go empty, it's taking forever, this is the second time in years that I am doing this.It's like the battery never loaded properly because of all the quick loading in between while it still had some power.It's like the shaving device never had enough power to do a good shave after only one maybe two times of usage.Has anybody else noticed this effect ?I believe the barbershop lady, she has many years of experience shaving lots and lots of people.Now comes the real question:What's going on inside the battery during these quick loads ?Why doesn't it load fully for good shaves many times ?Why must it be drained completely first for good/full loading ?After the shaving device is completely emptied and re-loaded I shall report back on how many good shaves I could do !Probably gonna take some weeks ;)Bye,  Skybuck.

miso · Accepted Answer

isingterotsrtAssuming nicads/NiMH, the battery has a limited number of cycles. Theintent is to get full cycles, so drain the battery. Empty is a poorterm since you don't want to discharge the cells below say 0.9V percell.Another advantage to fully draining the cell is it is less likely thatyou will overcharge the battery if the charger is a simple timer.For home use, just get a Philips shaver. They have great powermanagement.

Jim Thompson · Answer

I think this "deep-discharge-before-recharge" rule only applies toNiCad's.  Look up memory effect in NiCad's.                                        ...Jim Thompson-- | James E.Thompson, P.E.                           |    mens     || Analog Innovations, Inc.                         |     et      || Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    || Phoenix, Arizona  85048    Skype: Contacts Only  |             || Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  || E-mail Icon at  |    1962     |                  It's what you learn, after you know it all, that counts.

Martin Griffith · Answer

Since you are the computer whizz kid around here D/L GCC WinAVR and program an AVR micro to monitor the battery state and plot it out, then stick it on your blog.

BTW nimh don't really have the memory effect that you speak about

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martin

Robert Roland · Answer

It is called "Voltage depression". It is caused by overcharging the battery over time. Many commercial products have no charge control at all, and simply leave the charge on forever.

The effect is often confused with "memory effect", which has similar symptoms, but a different cause.

Electronworks.co.uk · Answer

The memory effect is only really applicable to NiCads. NiMH and Lithiums do not have this phenomena.

It could also be the gas guage inside the shaver. Some gas guages need the battery to be completely discharged so they can get a low reference point. Frequent short charge discharge cycles allow the errors to build up. A good discharge resets everything.

Bill Naylor Electronworks.co.uk - electronic kits for education and fun

Tip: Let battery go empty before reloading. Q: Why ?

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