Any use for old 3G flip-phone batteries?

[Rick Law]

Probably like many of you, I have a collection of old cell phone batteries.  For example, my 3G flip-phone are long since useless but the batteries are still somewhat good.  Throwing them out seem such a waste.

Looking for ideas to put them to some use.

So far, I "repurpose" a couple of my decade old (razr v5 3G flip phone) 800mAH range lithium battery as emergency (power outage) lighting.  Most of my flip phone batteries are down to 50% to 80% of capacity.  Still, 600mAH flip-phone lithium battery would give hours of lighting running at say night light level.  That little light is such a calming thing not to have to deal with complete darkness during occasional power outage.  But, I don't need half a dozen more of such emergency lamp and I still have more than a handful of old flip phone (<1000mAH) batteries...

Have you guys "repurposed" old lithium batteries?  Suggestions?  I like to explore what can I do with them other than using them to fill up unused capacity of my garbage can.

[Andy Chee]

I also have a handful of random phone batteries, alongside my collection of vape batteries.

Unfortunately I also have yet to find a use for them

[RoGeorge]

Yes, I repurposed a few phones, too.

Sometimes the entire phone can be reused as it is, for example:
- as a dedicated audio player (I use to play audiobooks in the background while doing house chords), or as a FM radio
- have a more recent phone as a photo camera, it sits on the lab workbench at all time (in airplane mode, so the phone won't waste battery trying to detect the radio networks around), and use it to quick take snapshots of the tech gadgets I might open and their PCBs because it takes good close-up photos and can be transferred to PC by Bluetooth, so no cable needed
- used an old Nokia as a battery holder, for its battery contacts, to test/charge Li-Ion batteries with the same step between battery terminals
- once desoldered and reused an oscillator
- there are drivers for the displays from Nokia 5110 and similar models, to reuse the display in other microcontroller projects
- some electronic gadgets made for working with a 3V button cell like CR2032 might run just fine with a rechargeable Li-Ion.  A Li-ion has max 4.2V instead of 3V, but if you suspect this might be too much, you can charge the Li-ion to only 3.8V, because not much energy is stored above 3.9V anyway.  A Li button cell, single use CR2032, may have as much as 3.3V when new, so you won't probably damage anything at the 3.8V from a rechargeable Li-ion.

It's nice that Li-ion rechargeables have very low discharge rate, one charge can last for years.  My weighting scale has more than a year with a 4.2V charged Li-ion instead of a 3V CR2032, and still working fine.  Never recharged it in the last 1.5 years, and it should probably last a few more years before needing a recharge.  After one year the voltage went from 4.19V to 3.96V:  https://www.eevblog.com/forum/beginners/li-ion-cell-instead-of-a-cr2032-for-a-domestic-wight-scale/msg5339312/#msg5339312  Calculated time to last on one charge was about 20 years. 

[kripton2035]

I have noticed that lots of batteries that you don't use for a while are prone to be almost dead ...
check your batteries with a tester, I'm sure half of them don"t hold a charge anymore ...

[Nusa]

I've repurposed one of my old phones as a dash cam. The free software to support that is out there if you look for it.

[RoGeorge]

Depends of the battery, some become unusable, but most are just fine, except they only have about half of their nominal capacity. The oldest still in use I have is a Nokia from about 15 years ago, from when there were no touch screens, has physical dial pad buttons.  Beeps to be recharged once a week.

I keep that phone because it has a very nice lap-timer, and a very easy to set egg-timer/alarm.  Great to remind when to stop heating the food while loosing the track of time browsing the web.  Another use of it is it can take audio notes with a press of a button, though recently I didn't use that very often.

In my use case, it happened that many of the Li-ion I have had for many years in storage, decided to swell almost all at once, in the same year.  I suspect this is because I charged them to 4.2V and stored them fully charged.  Since then, I only charge Li-ion to 3.7V before putting them in long term storage (long as in many months, or even years), and only charge them full if/when I need to power something.

What failed more often for me were the laptop batteries (the ones with typical 18650 round cells).  They should last longer, have their own internal battery management chips and all, yet after a while they do not hold charge at all.  I have had more luck with the single cells, flat and square batteries, from the old 3G mobile phones.  Though, the mileage may vary with those, too.

[NiHaoMike]

Get some cheap TP4056 modules and embed the batteries in projects.

[Rick Law]

I have noticed that lots of batteries that you don't use for a while are prone to be almost dead ...
check your batteries with a tester, I'm sure half of them don"t hold a charge anymore ...

Yeah, I normally tests "recovered" batteries first before I reuse them.  Besides capacity, safety is another factor.  I want to make sure it has a couple of uneventful charge+discharge cycles before I consider it as "okay to redeploy".

My general day today re-charger has capacity test.  For more details test, I have a home-made discharge tester based on the Arduino Nano and the INA219.

When it is fat (swollen), I dump.  When it is <50% I usually dump it but not always.  Some of my 18650 re-wraps are down to about 40%, but since it is already fully charged, it sits around waiting for "last use".

Not all damaged cells are swollen.  I had an old StarTAC phone battery that looked very normal at re-discovery but got very hot on post-recovery recharge.  Too hot to touch.  At light speed, I pick it up with pliers out to the backyard for safety, let it cool then dispose.  I did that so fast I did not even note if I had a connection error or was it a battery failure alone causing the heat.  That experience was a good "reality check" for me...

...
- there are drivers for the displays from Nokia 5110 and similar models, to reuse the display in other microcontroller projects
- some electronic gadgets made for working with a 3V button cell like CR2032 might run just fine with a rechargeable Li-Ion.  ...  My weighting scale has more than a year with a 4.2V charged Li-ion instead of a 3V CR2032, and still working fine.  Never recharged it in the last 1.5 years.
...

Interesting you should bring up the Nokia 5110.  It is the display I choose for my Arduino Nano discharge tester/logger.  Discharge done with the INA219, Nokia 5110 doing the display, and Arduino doing the monitoring as well as passing it on via serial to PC for logging the data.   At one time, I've about two dozens of 18650's recovered from laptop battery packs.  I use my discharge logger to determine if the recovered battery is worth the time (and cost) in adding a protection board and re-wrap.  Small display but rather handy.

Weight scale is a good idea!  I just replaced my old (analog) failed scale with a new digital one using 2xAA, this looks like a good potential user of old phone batteries.  The other is the digital clock near the weight scale that uses a pair of AG13, I may be able to use an old phone battery for that clock and forget about hunt for my AG13's every few months.

Get some cheap TP4056 modules and embed the batteries in projects.

Good reminder, if I want to add recharge in my adaptation of old phone battery into my gadget, that is a great little module for recharging.  I have a couple of those modules on hands.  After initial testing a few years back, they have been just sitting in my drawer while I forgot I even have them.

[johnh]

   Recycling

[Rick Law]

Funny how the brain works.  I have an old brain.  Stuff I've done long ago probably gone into archival storage and I didn't recall it as readily.  Thanks to this conversation for waking up some old memory, I suddenly (while in the shower last evening) remember this is actually the second time I approached this problem.  The first time was around a decade ago.

Then, I made a prototype, with 3x18650 sub-par capacity (below 50% of original) batteries, added a Schottky diode to each battery, then parallel the output after the diode and feed the combined output to a 5V boost converter to make a USB power bank out of my subpar 18650 batteries.  The Schottky diode before combining serves as "power selector" taking more power from the more capable battery.  After that prototype works, I found little use of it since I already have 3 good phone charger power bank.  That prototype board was put away somewhere in a box.

Now revisiting this problem, while a subpar power bank is not particularly useful but a high lumens "power outage" emergency light would be useful (power outage dinner prep light).  A higher lumens light for more safety while working with sharp kitchen knife.

I already know that "combining" the subpar 18650's capacity works well from my abandoned prototype, combing old phone batteries is no difference than combining 18650's.  Instead of the 5V booster, I can connect the combo output to a Cree XM-L2 mounted on an appropriate heat sink.  Running the XM-L2 or T6 at about 1A to 1.5A, that is more than enough light to prepare and to eat dinner.  By now I have "standardized" old phone batteries' output connector.  I've to hunt down that prototype box to make sure my old 18650's also adhere to my current "standard" and add them to the pool of subpar batteries.

I know I have some XM-L2, T6, and miscellaneous (Q5/XR-E/G2) LEDs at hand.  I think the Q5 could be bright enough and last longer.  Besides, the "Genuine Cree" LED stock I have at hand were all eBay purchases, only way to find out how bright it is would be to try it out...