3v rechargeable cr2032 batteries and charger - recommendations please

[Polar Bear]

It seems that our car remote key fob eats batteries.  6 months for a CR2032 lithium button cell.  My view is that I would rather have rechargeable if there is a suitable option out there.

Recommendations and advice on those to be avoided will be much appreciated.

Thanks.

[hbunnet]

I had a problem with that PB, when my wife's key fob also ate it's cell in a short time. I decided to change to new Duracells and the problem has gone away.

[rafletcher]

A year is about par for the course with decent Duracell batteries if you have keyless entry. Be wary of the rechargeable ones, a quick google suggests they lack the power of disposable ones, and that can be an issue.

[Diver300]

Things that use coin cells can be very dependent on the cell voltage. Some will work down to a very low voltage, while others will stop even though the voltage with no load is above nominal.

Different makes of battery may hold up the voltage better than others.

[robgul]

Am I missing something here? - the remote (door opening) key fob (only ever used one of them) on my last 4 vehicles over about 25 years never required battery replacements . .  current car is 4 years old, previous was 11.

[Polar Bear]

We have a friend with a 15 year old Toyota.  Both of his keys are still powered from "as new".  If you open up the key it doesn't have a replaceable battery but a sealed programmable module.  It simply has a lock and an unlock button and of course an oddly shaped blade of metal.  I wonder what that is for?

I think that the problem with the modern fob is that it seems to be "always on"* looking for your car so it can pair.  Many people love the function where it unlocks as you walk up but we prefer not to have that.  I mean, it's so uncool and irksome to have to actually grab the handle whilst the key is in close proximity to open the door don't you think ...  🤔

The consequence is that the battery burns through way too quickly.   Just another consequence of a consumerist, throwaway society.

I find myself now with a cr2032 in it's slim card-mounted plastic bubble tucked into one of the pockets of my wallet.  In an age where we are encouraged to no longer carry cash, cards and even phones now with the creation of eSIM call capable watches, ironically I need to have a spare battery with me at all times.

Sheer wasteful lunacy.

*  I am sure that those with better understanding can explain the technical shenanigans of this.

[Jaded]

Biggest problem with button batteries nowadays is getting them out of the plastic bubble…

[Diver300]

I think that the problem with the modern fob is that it seems to be "always on"* looking for your car so it can pair.
*  I am sure that those with better understanding can explain the technical shenanigans of this.

It's a bit like that. The keys that need you to press a button just send data blindly. The first ones were always the same code, so relatively trivial to clone. Then there was rolling code, but even that has been hacked*.

The keyless ones use a low frequency (125 kHz) signal to activate the key. That is much like the technology used for credit cards etc, but can be done a much larger range because the signal does not need to power the electronics, nor does the return signal need to be sent the same way. The return signal is the 433 MHz signal that has always been used.

Extra security comes from the fact that there is random challenge in the signal from the car, and the response from the key has to contain the correct response, calculated from the challenge**. The low frequency is picked up magnetically with three coils at right angles in the key, and the range of that can be controlled quite well, so that the keys will not detect the car at a long range, so more than 5m or so.

I agree that it's a pain that they use the batteries more than they used to. Some keys demand to be powered all the time, so if the battery is removed, they will lose their coding, which strikes me a missed opportunity when EEPROM exists. I've even seen a Lithium-Ion rechargeable battery, presumable to cover battery changes in keys like that, with a small dc-dc boost converter fed from the CR2032 to charge the Lithium-Ion battery.

I suppose that there will be advantages of iThing as a key which will be happening soon.

*Microchip KeeLoq® is an example.
**https://en.wikipedia.org/wiki/Challenge%E2%80%93response_authentication

[Polar Bear]

Apparently if you drive a Mini of recent vintage your key fob actually has a rechargeable battery within and you can charge this battery by simply putting the fob in it's designated place within the car.

What a very sensible idea and one that other manufacturers should be doing as standard imo.

I have ordered a charger and four notionally 3.7v rechargeable batteries.  The plan is to charge the batteries up and then do a volts and amps test against a new Energiser lithium cr2032 battery.  If all seems well I shall risk using one next time round.  Could be a very expensive mistake or could prove to be a long term money saver.

I note that Maxell sell rechargeable cr2032 equivalents rated at 3v just like a standard lithium cell.  Perhaps I shall buy some of those in due course to test.

[orienteer]

Biggest problem with button batteries nowadays is getting them out of the plastic bubble…

Agree! I think it should be a legal requirement for all packaging to be readily openable. Current situation apparently results in thousands of visits to A&E each year. Main reason I carry a penknife is for opening packaging.

[SoreTween]

What a very sensible idea and one that other manufacturers should be doing as standard imo.

BMW have for years, at least from E46 on so 1997. 5 & 7 might go back further.

[Kim]

Biggest problem with button batteries nowadays is getting them out of the plastic bubble…

Agree! I think it should be a legal requirement for all packaging to be readily openable. Current situation apparently results in thousands of visits to A&E each year. Main reason I carry a penknife is for opening packaging.

I note that they've deliberately beefed up the plastic bubbles on my last pack of CR2032 cells to stop children eating them.  Like a child's slowly hydrolysing digestive tract, I've yet to find a way into them that doesn't involve carefulling with sharp objects.

Apparently some of them now come with a bittrex coating, which arguably tastes worse than 3VDC across the tongue, but seems to cause bonus high-resistance contact issues.

Maybe we should just find better ways to power small electrical devices?

[rogerzilla]

Biggest problem with button batteries nowadays is getting them out of the plastic bubble…

Traditionally, we blame "stupid kids in America" for such H&S frustrations 

[Polar Bear]

The batteries and charger arrived yesterday.  The brand labelling is EEMB and the box says that the charger which seems a bit Heath Robinson to me was made in China.  Anyway, according to the led lights how on the charger all 4 cells charged.

This afternoon my man with a multimeter and a smidge of knowledge (as oppose to my layman's ignorance) is going to compare the volts and current? for the EEMB 3.7v cells against new in sealed bubbles 3v lithium cells, one branded Panasonic and one branded Energiser.

I am not sure what we will find but I will report back.