[EvaH (OP)]

Michael got in touch to ask:

Why can’t batteries such as AA and AAA size be recharged? What’s the difference between regular batteries and rechargeable especially lithium versions? Is this a “Big Battery” conspiracy to sell  more batteries, or are there valid reasons?

We'll be answering this on next week's show, but what do you think?

[alancalverd]

'Twas ever thus. The answer, in one word, is Chemistry.

[Winfort]

Rechargeable batteries are reusable power sources that can be recharged many times - at least several hundred times. This is less damaging to the environment, for which batteries are toxic.

Rechargeable batteries are in the same format as conventional batteries, most commonly AA and AAA. They are labelled Rechargeable and their capacity in milliampere hours (mAh) is indicated on the case. Rechargeable batteries discharge faster than rechargeable batteries, but make up for this by the number of recharging cycles.

To recharge rechargeable batteries you need a special device that you plug into an outlet. This is usually sold with the batteries. The most common rechargers are available for AA and AAA formats with the ability to charge two or four batteries at the same time. There are also universal chargers to charge all popular battery formats.

[Colin2B]

Rechargeable batteries are reusable power sources that can be recharged many times .........

While you were busy trying to spam us you might have had the decency to answer the question.

[katieHaylor]

This question has now been answered on the show. You can listen here - https://www.thenakedscientists.com/podcasts/question-week/why-arent-all-batteries-rechargeable

[VinsonPerez]

how Are YOU?

[Kryptid]

how Are YOU?

Please don't spam. This isn't the appropriate thread for that.

[CliffordK]

I have to think the answer is somewhat more complex than simple battery type. 

I'm pretty sure years ago I have recharged alkaline batteries.  One can often get a couple of charge cycles out of them, but they also have a tendency to leak, so I try to avoid using them too long.

Button batteries can be marketed as either rechargeable (for example LIR2032), vs non rechargeable (CR2032).  I think the anodes/cathodes may have slightly different chemistries, but one can often get a couple of charge cycles out of the non-rechargeable button cells.

The non-rechargeable batteries often have many more amp hours. 

I wonder if it is not as much of a chemistry issue, but rather a matrix issue.  So the anode/cathode doesn't get fully reconstituted with each charging cycle. 

This is also the reason why some batteries can last a very long time if light cycled, but can be destroyed quickly if deep cycled.

[Petrochemicals]

How, prey tell, do these work then?

https://www.amazon.co.uk/SBC1001-Battery-Alkaline-Batteries-Rechargeable/dp/B00872D8WU

[William Hardy]

Rechargeable batteries usually cost more than regular batteries.

[Zer0]

But... Considering the new upgraded models of Rechargeable Batteries...they are much more Economical & Reliable & Environmentally Friendly & last longer.
👍
(NiMH)

Buying a pair of brand new Alkalines on Ten different occasions would be a Total of 20batts.
(Figure out the price of a pair & multiply it by 10)
🔋🔋🔋🔋🔋🔋🔋🔋🔋🔋
🔋🔋🔋🔋🔋🔋🔋🔋🔋🔋
& Now Compare it with the Price of a Single Rechargeable Battery which can be Reused approx 100 times.
(Add on your Electricity consumption to it if you wish)
🔋🔋
And the Answer would be Self Evident.
(Epiphany)
🎧



*Warning* - Rechargeable Batteries ideally are NOT Recommend for Smoke Alarms & Emergency Kits.
🖖

[Eternal Student]

Hi all.

  Another minor difference is that I find rechargeable batteries, after a good charge and when they are still quite new,  offer slightly more low down torque in my radio controlled cars.

    I've measured the voltage of the rechargeable AA and it is pretty much 1.5 V  just like a new non-rechargeable AA, so it's not that they are producing a higher voltage.  (That would be cheating anyway).

    However, I think the internal resistance from a new rechargeable is slightly lower than a standard alkaline non-rechargeable AA.  So you get just that little bit more of the 1.5 V  dropped across your electric motor instead of heating up the battery.  It's most noticeable on the acceleration, when the electric motor is almost static and acting just a piece of wire with resistance in a similar order of magnitude to the internal resistance of the battery.  The top speed of the cars is not affected, since the back emf from the motor is killing the voltage from both sets of batteries equally.
Anyway, it's enough to get me half a cars length ahead of my son.

[alancalverd]

The lower internal impedance of rechargeables is particularly important for power tools as it allows higher stall current and torque than can be achieved with the same size primary cell. Used with a "joule thief" inverter, you can also turn more of the theoretical stored energy into useful energy at constant voltage. 

Most primary cells can be recharged a few times by adding a bit of AC ripple to the charging voltage. It's a black art that has largely been superseded by efficient rechargeables but various gadgets for maintaining primary batteries were popular in the 1970s because 4 x 1.5V cells was cheaper, lighter and had better energy density and less standby leakage than 5 x 1.2 V NiCads in a walkie-talkie. 

[yapimop]

Does anyone run rechargeable batteries in their remote? Are lithium or NiMH better for remotes? Are any particular brands better than others?

Any advice will be greatly appreciated! Thanks!

[alancalverd]

The "active" energy drain on a remote control battery is generally negligible compared with its self-discharge, unless you are an inveterate channel-hopper, so the battery with the lowest self-discharge will give you the longest effective service. In my experience most televisions get replaced by the time the remote is on its second set of good quality alkalines. So you need to factor in the capital cost of the batteries and the charger (which you might use 4 or 5 times per TV set), the frustration of looking for the charger when the remote ceases to function, and the aggravation of having to wait for them to recharge before you can switch the TV on again.

Folk who rely on rechargeables for important functions (builders, orthopedic surgeons....) keep one set on charge whilst using the other, so you need to shell out for two sets of batteries and keep the charger running in standby mode. All money down the drain, even if it's "green" in the long run.

[Bored chemist]

so you need to shell out for two sets of batteries

Do you recognise that "two" isn't very many, but the number of primary batteries you would need is "a lot more"?

[alancalverd]

As I said, about four AAA cells per television. Two of them are delivered with the telly anyway. Compared with four rechargeables which may last a bit longer (the number of discharge cycles is irrelevant: what matters in this application is their  corrosion and internal degradation lifetime) if you are lucky.

Obviously nobody would use primary batteries for a drill, nailgun or bone saw, but the question was about TV remote controls.

[Bored chemist]

the question was about TV remote controls.

I missed that bit .
"Why can’t batteries such as AA and AAA size be recharged? What’s the difference between regular batteries and rechargeable especially lithium versions? Is this a “Big Battery” conspiracy to sell  more batteries, or are there valid reasons?".

Also, did you know that you can use the same set of rechargeable batteries in your new TV remote?

[SeanB]

There is a triangle between current capacity, lifetime before discharge, and cost. A cheap AA or AAA cell has a low capacity, but it will in general last for 5 years in a remote control, with a very low average current draw, equal to the self discharge current in the most case, and it only has to supply brief pulses of current a few times a day to operate the IR LED used to communicate to the TV set. A poor candidate for rechargeable cells, as they typically are optimised for high cycle count for charging, and low internal impedance, so self discharge on them means they will go flat in under 6 months, unless designed to minimise this, which adversely affects cycle life and discharge current. Thus a primary cell is best here, low cost and good enough.

Contrast this with say a toy, or camera, where there is a heavy load, and a rechargeable cell wins out, low impedance, decent enough capacity, and charge cycles are enough to last a few years in use. Primary cells do not last long here.

Also you do get rechargeable alkaline cells, which swap capacity for charge  ability, in that they have much thicker cases, so as to handle the high pressure evolved inside, and also have thicker electrodes, so that the reaction can be reversed without causing the thin casing to erode away. The reversal is possible on regular cells, but they can only be partly recharged, as the optimised construction for highest capacity at a cost point means there is no extra electrolyte available to be consumed in the end of charge reactions, when hydrogen is being produced internally in the electrolyte, as there is little dissolved active material left. You can get partial recovery, provided you have not used around 30% of the capacity, and each cycle you only get around 80% back, though you have to put in 200% of the energy to reverse the reactions internally, as opposed to the rechargeable NiCd or NimH which is overall able to go to zero charge per cell. But absolutely no reverse charge, which destroys both primary and rechargeable cells. There you get around 75% of the charge in coulombs back, though there you need to charge slowly, so as to allow the chemistry to complete without heating up, otherwise fast charging (anything short of 12 hours per cell, at a current of 10% of the rated capacity in mAh) will generate a lot of heat, which reduces cell life by degrading separators, growing dendrites of the active metals and also generating hydrogen and oxygen gas, which can vent from the cell, removing electrolyte from the cell.

This applies to the common cell types, Zinc carbon and alkaline primary cells, and Nickel cadmium or nickel metal hydride secondary cells. You also get lithium based cells, also available commonly as a primary coin cell, like CR2032, or as lithium rechargeable cells in various chemistries, like pouch cells commonly seen inside equipment and ecigs, cells like the 18650 cell so common in torches, and also prismatic cells like used in mobile phone removeable batteries. Those are definitely all different, and need special care taken with them, so are not really a consumer useable product without understanding the safety and handling required.

[Robida]

Michael got in touch to ask:

Why can’t batteries such as AA and AAA size be recharged? What’s the difference between regular batteries and rechargeable especially lithium versions? Is this a “Big Battery” conspiracy to sell  more batteries, or are there valid reasons?

We'll be answering this on next week's show, but what do you think?

Chemistry is different. As i know, for rechargeable batteries: NICD NIMH Li-ion zinc lithium......, for non-rechargeable batteries: alkaline, LISO2, LIMO2.....