Lithium Coin Cells and Car Entry Key Fobs

[Jon_G4MDC]

These are common today, and after about 3-5 years the battery says it needs replacing. I have had 2 recently that were not so simple.

First one was a CR1620, not that easy to buy as the main supermarkets don't stock them. I bought one from somewhere we call the plastic junk shop which has been OK in the past for watch batteries and such. It was a Renata and looked OK enough.

On fitting that the Fob would not TX - has an LED to show it is working - dark. Car remains locked - worrying in case of losing synchronisation and all the pain that entails. Battery out, terminal Voltage is 3.2V, seems not much wrong? Back in and out several times - just does not work. Bought another one from elsewhere all OK. I forgot about it.

Today the fob for my own car was giving whinge about low Voltage. Lazy as ever, I recalled this one was a CR2032 and I have some of those squirrelled away from my last car. A bit old but having just sat on the shelf should be good for a year or more - No? No. It measured 3.3V but on fitting it the car stayed locked. Looked for TX RF from Fob (no LED on this one) - nothing. Put old cell back - car unlocks/locks fine. Hmmmmm

Not having another CR2032 I thought to try something different. Put a load on it - what then? The only thing I could find was a 3V LED bulb for a Maglite. Might as well try. It flashed very briefly then went out - bad contacts? Try again - it flashed a bit longer. After a few cycles of this it stayed lit at decent brightness. I put it back in the fob and it works - how long? We don't know...

It seems Li coin cells develop high internal resistance when stored for long periods. A load will chivvy them back to life. I have lost the CR1620 from Fob #1 - I would like to have the opportunity to see what would happen with that one.

Here is a quotation found online "Once a load is placed on the battery, the passivation layer will become thinner, and internal resistance typically returns to normal."

I wonder if anyone knows about this effect?

Mods if this should be in modern technology please move....
In hindsight might not have been the best section.

[Philips210]

Hi.

That's a strange property and thanks for pointing out your experience with the coin cells. ISTR having had a similar unexplained problem with lithium cells fitted in the transmitter of a wireless doorbell. That could well have been an internal resistance issue.
Relating to computers, and in particular the lithium CMOS memory retention cell, I wonder if it's also worth giving it a brief but moderate load before installing it. This I suppose will ensure reliable operation and perhaps a longer service life.

Regards
Symon.

[jimmc101]

This is normal behaviour with Lithium cells and as you say is known as passivation. e.g. passivation in lithium batteries
It's what gives them such a long shelf life. They will recover after being under load for a while.

Jim

Better link http://data.energizer.com/pdfs/lithiumcoin_appman.pdf (page 6)

[Jon_G4MDC]

Most interesting & thanks for replies. It must help sales!
It seems in very low current applications, such as memory retention, it is not too much to worry about.
I will keep my LED to "jazz them up" for use in car keys.

[MotorBikeLes]

Quite a few people fit lithium batteries on off-road motor 'bikes, being much lighter than lead acid, and lower AHr sizes can be used in view of the higher cranking current. However on cold days they may refuse to turn the engine over. Switch on headlights for a short period, and then they will start OK.
I did not realise it applied to Li-ion cells. What is the mechanism connecting long storage and low temperatures?
Les.

[emeritus]

An ex-Royal Signals engineer at Plessey told me that in the depths of winter they had to briefly short their tanks' batteries with a large spanner before attempting to crank the engine. The brief short circuit warmed up the battery, increasing the chemical activity and avoided flooding the engine by abortive starting attempts.

[Bazz4CQJ]

I'd guess that tanks must use big lead acid batteries? Is it the case with lead acid that if they have a constant light load (such as the security/locking system in a car) you get a polarisation effect of the electrolyte adjacent to the plates, so even after a period of 'some days' and with a battery you think was OK, when you try to start up, the battery may not manage it? I read somewhere recently that the current drain in some modern cars, when static, is becoming a problem. I'd never thought of applying a short in order to 'energise' a battery!

B

[Terry_VK5TM]

I read somewhere recently that the current drain in some modern cars, when static, is becoming a problem.

Not only modern cars.

I have a 1986 E30 BMW with one of those stupid little DIN batteries, that if the car is not run for 3-4 days, refuses to crank the engine.

Terry

[lesmw0sec]

Originally Posted by Philips210

Relating to computers, and in particular the lithium CMOS memory retention cell, I wonder if it's also worth giving it a brief but moderate load before installing it. This I suppose will ensure reliable operation and perhaps a longer service life.

You have given me food for thought here - I have an old computer that insists that there is a CMOS error and takes me to the BIOS each time it is switched on. The battery was flat and I replaced it with the same problem present. Might try the blighter with a load as suggested!

[PsychMan]

I threw out one of those cheap stylus pressure gauges due to a similar problem.

Come to think of it, the fella in the shop who sold me the replacement batteries did sell them cheaply on the basis he'd "had them on the shelf for years"! Wish I'd tried sticking a resistor across them now.

Thanks for the tip I will remember that

[MrBungle]

I've encountered this before. They don't always recover when you apply a load. Probably a 50-70% success rate. Worryingly enough I've seen it with new ones from Tesco. Source impedance on one was about 200 ohms!

When I was a kid we used to toss them in a frying pan in the kitchen when they went flat for a couple of minutes. If they didn't blow up, which was fun anyway, they'd work for a few more days once they'd cooled down. I wonder if that had the same effect.

[Philips210]

Originally Posted by MrBungle

When I was a kid we used to toss them in a frying pan in the kitchen when they went flat for a couple of minutes. If they didn't blow up, which was fun anyway, they'd work for a few more days once they'd cooled down. I wonder if that had the same effect.

Blimey! I wouldn't try that especially a lithium battery. I don't think I'd want to eat anything cooked in that frying pan

It's good that the OP has brought this internal resistance problem to our attention. Whilst several members already knew about the shortfalls of lithium cells, many didn't and a lot of us including myself will now be wary of the problem.

Regards
Symon.

[Bazz4CQJ]

As an alternative to using a load to break down the passivation layer, which will use up a bit of the cell's power, I wonder if the layer could also be broken down by connecting the cell to an external PSU and putting a few mA in for a few seconds (with due regard to H&S!)?

B

[MrBungle]

I'd stick your fingers in your ears if you do that. They go with quite a bang!

[Bazz4CQJ]

...emphasis on "few" mA seconds... and it still has to overcome the passivation layer, so if it's only a slight over-voltage you'd see the current slowly increase? Surely safer than a frying pan ?

[kalee20]

Originally Posted by Bazz4CQJ

As an alternative to using a load to break down the passivation layer, which will use up a bit of the cell's power, I wonder if the layer could also be broken down by connecting the cell to an external PSU and putting a few mA in for a few seconds...

In that case, the current would be flowing in the opposite direction. Would it not tend to plate on a bit more passivation, rather than take it off?

Cards of lithium coin cells are available from Poundland - a cheap way to do a trial!

[Jon_G4MDC]

Benny Hill sang...
I'll stick my fingers in my ears and say Ting-a-ling-a-loo...

Pleased it has got the investigative juices flowing. Be safe.