why do you have to wait until a rechargeable battery is almost spent before recharging it ?

Question

i was told i shouldn't recharge my phone until there's only one or two bars left of power as it damages the battery. Is this true and if so, why is it true.?

Answer 1

NiCad batteries have a power memory. If you discharge them half way then recharge, they discharge only to the half-way mark and fail.

New Lithium-Ion batteries don't have this problem. But, they can be damaged by fully discharging them. So, in a way, you still need to keep track of your battery.

The worst part are Laptop batteries. Some have chips in them that have an expiration date. When your battery reaches this date, it stops working. You have to buy a new battery. Too bad the French outlawed the guillotine as these execs who came up with this idea to sell more batteries ought to be taken care of.

Answer 2

That mainly applies to nickel cadmium batteries. Don't know if it is true.

Quote wikipedia
"It is sometimes claimed that NiCd batteries suffer from a so-called "memory effect" if they are recharged before they have been fully discharged. The apparent symptom is that the battery "remembers" the point in its charge cycle where recharging began and during subsequent use suffers a sudden drop in voltage at that point, as if the battery had been discharged. The capacity of the battery is not actually reduced substantially. Some electronics designed to be powered by NiCds are able to withstand this reduced voltage long enough for the voltage to return to normal. However, if the device is unable to operate through this period of decreased voltage, the device will be unable to get as much energy out of the battery, and for all practical purposes, the battery has a reduced capacity.

There is controversy about whether the memory effect actually exists, or whether it is as serious a problem as is sometimes believed. Some critics claim it is used to promote competing NiMH batteries, which apparently suffer this effect to a lesser extent. Many nickel-cadmium battery manufacturers deny the effect either exists or are silent on the matter.

The memory effect story originated from orbiting satellites, where they were typically charging for twelve hours out of twenty-four for several years. After this time, it was found that the capacities of the batteries had declined significantly, but were still perfectly fit for use. It is thought unlikely that this precise repetitive charging (e.g. 1000 charges / discharges with less than 2% variability) would ever be reproduced by consumers using electrical goods.

An effect with similar symptoms to the memory effect is the so-called "lazy battery effect." (Some people use this term as a synonym for "memory effect") This results from repeated overcharging; the symptom is that the battery appears to be fully charged but discharges quickly after only a brief period of operation. Sometimes, much of the lost capacity can be recovered by a few deep discharge cycles, a function often provided by automatic NiCd battery chargers. However, this process may reduce the shelf life of the battery[3]. If treated well, a NiCd battery can last for 1000 cycles or more before its capacity drops below half its original capacity."

Answer 3

batteries create something called "battery memory"

It is like the ring in your toliet (really gross comparison I know)
The ring signifies where the water level is at usually. In a battery this "ring" miscommunicates to the battery charger indicator that there is only the amount from the RING (your current battery level) to the new recharged level available for use. When you plug in your phone, the charger doesn't PULL the remaining charge out and then refill the battery.

The basic premise is that if you recharge a battery before it's mostly spent, the battery will "remember" the capacity at which you recharged it, so you will have reduced the capacity of the battery.

Answer 4

Because the Ni Cad batteries ....the most common and now the least expensive .... have a memory and if you recharge it when only 1/4 depleted the battery will only hold 1/4 of a charge since it "thinks" that when it reaches the 1/4 point it is discharged .... the newer Lithium Batteries are not like that and have no memory effect so you can charge whenever convenient ....

Answer 5

Some batteries have whats called a recharge memory. If you usually charge the phone when it is half way empty, it will get used to taking half a charge. Therefore when it is empty it will still only take enough to charge it halfway because thats how much the phone is used to taking in. It is recommended for these kinds of batteries that it not be charged until its empty to get it used to taking in a full battery's worth of charge.

Nowadays, most phones don't need this.

Answer 6

Justin H is right - the batteries have a memory and so if you let them run down to, say half way, before charging them they will stick at this level and you will only ever get half of the battery life. It's better to let a battery fully discharge ocassionally.
The only thing I would comment on is that it's a really good way for the manufacturers to make you keep buying their batteries. You can buy batteries without memories.

Answer 7

I seem to remember that certain rechargeable batteries have a memory. If you only discharge it to 50% of its fully charged state continuously, then it 'thinks' that 50% is empty because it's never been lower! Sorry to give the battery human characteristics! You don't have to discharge fully every time, but should make a point of doing so, say, once a month.

Answer 8

It depends entirely on the battery technology.

NiCd batteries have a memory effect - their recharge cycle shortens if you do not let them fully discharge.

Some batteries have a maximum number of recycles. NiMH are like this.

But most phones use lithium ion batteries which have neither - they simply have a fixed life from manufacture, whether recharged or not.

Answer 9

It's called the 'memory' effect, in a nut shell, the battery remembers when it was last charged, and think that is it's empty level for next time! Most modern batteries don't suffer from this anymore

Answer 10

answer...it used to be...

the first generation of rechageable batteries did have a memory built into them, you could keep running the battery down and clear it out eventually but if you only let it run down say 80% everyday, it would goto 80% then the chemical that never reacted before wouldn't know how to get started to continue making the elctricity...

todays batteries are a lot better so you don't have to worry about it.