battery ressurection

The batteries (two AAs) in my walkman died to the point where it didn’t work at all. I switched them around: no change. So in my fridge, I find I have only one AA battery. I pop it in (with one of the “dead” batteries) and voila! the walkman works again.
Why does this work? And why does switching around a couple dying batteries sometimes work also?

Double As are meant to hold 1.5 volts of electricity when fully charged.
This means that your Walkman needs three volts (2 x 1.5) of electriticy to run optimally. Luckily, many electronic products can work pretty well at a lower voltage. However, at some point there is simply not enough power to crank the tunes. I’m afraid I don’t know what that is for your Walkman but – and I’m guessing here – it’s probably around 2.1 volts.

(Unless things have changed in the last couple years, rechargeable batteries only hold a charge of 1.25 or 1.3 volts. This means that a standard three volt personal stereo is operating at 2.5 or 2.6 volts on fully juiced rechargeables. For those of you who were wondering, that’s why rechargeable batteries never last as long as their standard, one-shot counterparts.)

Combining a relatively fresh battery with a tired counterpart may create enough combined voltage to revive your Walkman. So, if the weak one’s kicking out 1 volt and the strong one’s packing a healthy chrage of 1.6 (yes, fresh batteries can sometimes be over-charged) then you’re sitting on a healthy 2.6 volts of music blasting power – about the same as you’d have with fresh rechargeables.

If you were using the walkman at the time I have an answer. Batteries have internal resistance. When they are used they get hot and the internal resistance goes up. The voltage goes down. When you placed them in the freezer the batteries cooled down and the internal resistance went down. Your voltage went up.

I don’t know why switching batteries sometimes ‘revives’ them. I believe ya though because I have done that and switching around works sometimes.

By moving the batteries, you “scrub” the contacts, removing what little resistance there is, and supply a slightly higher voltage.

the way I recall i rfom HS Analog electronics class, by reversing the polarities of the batteries, you change which is the anode and which is the cathode.

In doing so, you rid each of the little bubbles of polarized hydrogen (?) that block the current (a byproduct of the chemical reaction) and cause the battery to “run out”. To increase this effect, tap the batteries, gently but firmly on a hard surface before reversing.

On low drain devices, like a remote control, you can keep doing this for years.


I was trying to see if I can find anything regarding the possibility that if you run a battery down, then let it sit a while, it will rejeuvinate itself a little bit so as to operate a little longer. I seem to observe this phenomenon all the time. but I found none so far. But I came across this link that gives great practical information about batteries:



Well… no it’s not. The amount of “charge” as you refer to it, is measured in watt-hours (or amp-hours when the voltage is assumed), not volts. Lower voltage does not imply lower capacity.

Ni-Cads (the most popular consumer rechargables) don’t last as long as alkalines or normal zinc batteries because they have a lower energy density, not because they have a lower voltage. For example, an alkaline C cell is about 7 amp-hours, while a high quality Ni-Cad C cell is only about 2, and a cheap one perhaps only 1.5.

Also, Ni-Cads have a lower internal resistance than non-rechargeables, so in some applications their lower voltage (about 1.2v compared to 1.5v) can make less difference to the operation of a device than you’d think based on the ratio of the voltages alone.

peas on earth

Thanks for catching me on that one, bantmof. I used to work in a consumer electronics store and that was the line they had us give the customers. I should know better than to trust any corporate entity that forces their employees to wear red, polyester, V-neck sweaters.


Slight twist here but why is it my rechargeables just die suddenly but regular batteries just die slowly.

For instance in a walkman with rechargeables I’ll be listening the music sounds fine, then suddenly it stops and the whole thing is dead.

But in the same walkman with regular batteries, the tape slows down, the music is distorted (from the tape not running as fast) and slowly the walkman dies over a period of days sometimes.

Assuming that your NiCds are healthy (see below), then it’s probably because NiCds have a very flat voltage vs discharge curve. Batteries do not necessarily have a linear relationship between voltage and remaining capacity, although non-rechargables tend to be close. One can plot these two things on a graph so that one can attempt to deduce the remaining capacity by measuring the voltage under some load. With NiCds, the voltage remains almost the same throughout most of its discharge cycle, dropping rapidly from (about) 1.2v to about 1.0v near the end of the discharge cycle. (And one should not attempt to discharge a NiCd to lower than 1.0v - you can damage it due to cell reversal). Nonrechargables, OTOH, have a more linear plot, so that as the battery is used up, it’s voltage decreases somewhat steadily throughout.

The reason for the difference is due to the electrochemical reactions inside the battery. Somebody who knows more chem can probably give a better answer, but here’s my wild-assed guess: In rechargeable batteries, different oxidation states of the anode and cathode do not result in loss of the anode/cathode material; all that happens is that valence electrons are lost or gained. The oxidation (or reduction) potentials of the unoxidized material remains the same, so the overall cell voltage remains similar until there are very few left to oxidize. But in non-rechargeable batteries, discharging it changes the actual concentration of materials, and the electropotential varies with the concentration. Consider that a guess and subject to correction by anybody with a chem background :slight_smile:

Anyway, properly treated, a NiCd should be good for 1000 or more cycles, but consumer ones rarely reach this because it’s very easy to abuse them via overcharging, cell reversal as a byproduct of over-discharging the battery, and so on. If you want your NiCds to last a long time, first and formost do not overcharge them - this is what kills virtually all consumer NiCds. The alleged “memory effect” is real but almost never encountered outside of commercial applications because it requires a very specific set of circumstances that don’t tend to occur in consumer use. What is usually mistakenly attributed to “memory effect” is really voltage depression due to improper treatment of the battery via overcharging or cell damage due to voltage reversal.

If NiCds are not healthy, then since the voltage-vs-discharge curve is so flat for NiCds, a little bit of voltage depression can cause consumer devices that measure the available voltage to measure too low an amount and cut out, causing the device to quit when quite a lot of charge is remaining in the battery.

peas on earth


You mean to say that if I tap my dead batteries in my remote, then put them in reverse, they will be back to full power?

Yeah, that reversing of polarity bit doesn’t make any sense, at least on electronic devices. Even if they have a diode bridge, so that they can be used with the batteries in in either polarity, the battery current still drains in the same direction.

I don’t know what kind of rechargeable batteries and charging circuit they use in Braun shavers, but they recommend completely draining the batteries, with the normal load of the shaver use, every 6 mo.

Ray (no expert on the black magic of batteries)

Well, it wont be as powerful as the day they were new, but they will definately work again (try it & see)

slot 1: - +
Slot 2: + -

put the battery in slot 1 into slot two and vice versa. DONT turn the batteries against the polarity indicated.

Maybe my explanation of why this works was harebrained (like I said, I was reaching into the past). But it does work on low drain devices, and temporarily on high drain devices (ie walkman)

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DW3, I actually looked at those two sites already. The phenomenon I am referring to would require that the chemical reaction in the battery somehow reverses itself somewhat if let to sit for a while, thus providing a little bit more voltage afterwards. I.E., radio dies -> turn off radio and wait -> radio works again for a very short while -> turn off radio and wati … etc. until there seems to be nothing left in the battery.


The answer is in there. It is infered though.
You can find more sites in a search engine. Use “measurement of internal resistance” as your keywords. The problem with that is you will hit sites of students pursuing an engineering degree and they will use language and formulas that are hard to understand. Using just “internal resistance” in a search will get a lot of websites to wade through. Maybe one will have the answer you’re looking for. Duracell use to have an excellent faq on this but they have changed their site alot. I’m still looking at their site to see if it is still there.

BTW I missed an important point. While batteries drain from use its internal resistance goes up. So it is more than a heat problem.