Testing smartphone batteries

Hello everyone,

let's share some test results (test data, or charts created by PCLS/DEX/LVS/Excel/etc) of our 3.6V 3.7V 3.8V rechargeable batteries at home, i.e. single cell non-cylindrical lithium-ion (or single cell lithium-polymer) batteries like the one used in our smartphones. It's hard to source official public pdf datasheets for such batteries and i haven't seen many internet reviews/tests of smartphone batteries. Btw my el cheapo USB tester gives comparable results but how fun is that?

My old phone battery (Samsung B800BC 3200mAh, hardly in use for 12 months) has been cra**ing out on me and before i substitute my spare battery (Samsung B800BE 3200mAh, never used) i wanted to compare their performance visually. I've been working with various battery analyzers (Imax B6, iCharger, B6 Mini, EBC-A, EBD-Mini, CBA, MH-C9K) and today i am showing how the MC3K could be misused for this purpose :devil: with a typical charging harness from the RC hobby folks.

WARNING: When handling a charging harness, there is imminent danger of short-circuiting the battery! As soon as a battery is connected, all wires and terminals of the harness are hot. This is especially true for the banana plugs. So DO NOT copycat the below setup, it's for instructional purpose only

Let's get started. I took three silly photos which should prove that my spare battery was new, unopened, untouched, unused. Interestingly the 4 mini contacts had traces of usage, maybe from QC ex factory:


This is what my new battery looks like:


and what my old battery looks like:

The nominal specs are the same, 3200mAh capacity, 12.16Wh energy, 4.35V Samsung, cell made in Korea. Model name B800BC versus B800BE shouldn't make a difference in testing, the letters could indicate sales or NFC region or whatnot, i dunno. The battery size dimensions is approximately (mm) 80.1 x 52.9 x 5.4.

I use the crocodile alligator clips to connect the harness with the charger. For the positive terminal a conductive spacer helps with the grip:


The battery has to be placed next to the charger, "external". Maybe standing in an upright position:


Or maybe lying on the side edge without a holder or support:


Or with some clamp or holder:


I don't like the upright standing position. It exerts too much stress on the solder joint, see the kink at the black wire terminal:


The hooks have more natural access to the battery lying on the the side edge:


Here a profile shot from bird's eye view:


And again some close-up views:

Btw credits for the hooking idea goes to a geman boardie, i stumbled upon it last December and immediately thought of testing it on my new mc3k unit.

The following pic shows my original Samsung 4.35V cradle charger and the USB tester. My new battery gets charged to 4.360V in the cradle charger, whereas the old battery somehow does not get charged higher than say 4.260V: the cradle charger and the phone's internal charger terminate charging at 4.22V, and the mc3k would return a Connection Break error at some late point during the CV-phase ("0 Volt"). Charging the old battery with 4.260V TARGET VOLT would finish without error. Maybe the old battery has some confused overcharge protection circuit PCB? I also get a Connection Break error ("0 Volt") with the new battery when discharging it lower than 2.775V, especially with a low discharging current like -0.20A. I like my gadgets in white:


The following Excel chart shows the capacity graphs in the traditional voltage-vs-capacity format in high resolution high accuracy. With this chart at hand, we can make three observations: 1) the old battery s*cks compared to the new battery, 2) the new battery is still far away from the nominal 3200mAh capacity, 3) the graphs look legit and beautiful and much finer and higher resolved than by any other of the aforementioned battery analyzers!


I logged lots of discharge cycles with the mc3k and or PCLS. In some runs the PCLS log was missing the last 4-6sec of data, making the log have an incomplete ending. Might be a bug in PCLS but am not sure if it can be remedied. PCLS logs the voltage and current with 1mV and 1mA resolution but capacity only with 1mAh resolution because of the digits space limitation on the LCD. Internally the device calculates the mAh's correctly with higher frequency and resolution as verified by rough calculation, 0.20*1000*(14*3600+50*60+33)/3600=2968.5mAh, and by Excel integral method:



I recharged the battery with the Samsung cradle charger or with the mc3k, usually without logging in PCLS. Here some arbitrary charge log of the new battery:


And of the old battery, on the same time frame:


The physical law "Discharged capacity = Charged capacity" was especially true for the old battery. Here the complete set of runs in chronological order over the past 2 weeks, the actual table.txt file i've been working with:


That table looks like excessive testing, unnecessarily so you think? Sure. But only repeated test runs will give us an idea of the consistency, tolerance, variation, or accuracy of the results. In future we will know what to expect, if we redid a particular test run and were unhappy with the result.

On a side note, the smartphone discharges the battery to 3.51V only, not further down; a battery with 3.51V offline voltage hardly gets the phone to show any sign of vital reaction when the on/off button is pressed. A battery with 3.50V offline voltage makes the phone look totally dead. So for practical purposes one could look at the capacity ("Discharged capacity = Charged capacity") between 3.51 and 4.35V only and use the USB meter to analyze the charged capacity. Yes the above table.txt showed that the USB meter reading isn't too far off from the mc3k reading. However, even if the USB meter measured capacity very accurately, the readings will still differ notably between recharges because the discharged capacity depends on the phone usage (high current draw vs. low current draw).

If you too have old or new single cell non-cylindrical batteries and want to test them with your battery analyzer, you're welcome to share the results in this thread. It's imho a fun exercise to analyze the battery when it's new/unused and re-analyze it after a couple of months. Me too, i'll definitely keep an eye on the rate of degradation of my new phone battery, which probably costs only 5$ on ebay new, so why bother?

Not bother. It's "most joyful".

EDIT:
2016-03-22 "2537mAh" charge "1.68A" from 3.510V to "100%" in Samsung phone (=4.318V, checked with DMM)

300 views, no peep, must be an interesting topic lol. let's revisit this thread to add new/other cell phone batteries or to check degradation of the previously tested batteries. today lemme add a brand-new phone battery, i got the Samsung Galaxy J5 from amazon and before testing the phone i grabbed the battery and tested it. hehe.

freshly opened amazon package with the battery taken out of the sealed J5 retail box:



let's open the sealed battery mini bag tütchen:



but wait, can we tell yet if there are marks on the pin contacts? imho there shouldn't be any. golden phone in the background:



no there aren't any, not really. with a microscope one could see something, sure:



so what kind of battery is in my EU market version of J5? label says EB-BG531BBE. This long ugly model name includes information on the coding of the NFC chip inside the battery. ebay search term < J5 samsung battery > results in a few hits with the same 2600mAh cell inside but with slightly different model name. the battery is samsung made and can be charged up to 4.35V (in theory):



the setup is the same as before. these photos are for my future reference when i want to re-test the battery and forgot how to setup the wiring:



with the flashlight holder clamp the battery has a firmer stand:



out of the box the battery came with 3.8V or so, can't remember. assuming C=2600mAh, i charged it with 1.30A (=0.5C) and Zero termination (~8mA), followed by a 0.52A discharge (= -0.2C) down to 2.78V. after a short pause i recharged the battery:



my mc3k engineering unit measured over 2600mAh, what?? for the 2nd test run, i discharged with -1.00A:



again over 2600mAh, not bad. for the 3rd test run, i discharged again with -1.00A:



similar result as before. have you also noticed that the recharged capacities are almost the same as the discharged capacities? for the 4th and last test run, i discharged with -2.00A:



aha there we go. looks legit. here a summary of the 4 test cycles, my original notes as saved on hdd:



as noted, i managed to log a few test runs with PCLS. for this, i used the brand-new USB data cable which was included in the J5 retail box . the x-axis and y-axis are unchanged compared to my previous post (OP), helpful for direct comparison:



charge curves will always look different because the graphs vary with the starting voltage. as you know, battery voltage recovers after a standard discharge. therefore imo it'd be pointless to compare charge graphs. here is one logged charge curve anyway:



please don't wonder why the buttons on my charger look so worn. they aren't. my buttons have recessed symbols and i filled them with white edding ink.

here the original PCLS log of the initial charge and 0.2C discharge, anything which strikes you in the graph?



again the question, does it make much sense to analyze smartphone batteries?

answer: not much, because as my previous post had shown, a usb meter is good enough to measure charged capacities between voltageA up to voltageB (= 4.35V, for example). and since < recharged capacity = previously discharged capacity > holds true for liion batteries, there is no need to discharge-analyze a phone battery with a hobby charger (or mc3k). this time, with the J5 battery, there was no surprise. label stated 2600 nominal, and there was over 2600mAh in the battery. however, with the 2 batteries from the OP, things were different, not anywhere near the 3200 nominal!

we'll reanalyze these batteries after months of usage. a USB meter can tell the degradation in numbers but not visually graph it for our enlightenment, cheers.

Very cool. FYI, ZeroLemon makes extended cells for smart phones that have removable batteries. In the realm of 8000-9000 mAh, I have one for LG Optimus G Pro and it's very nice. Triples your runtime.

I've had it for 6+ months and it's beginning to get tired after daily charge cycles, loses capacity. You charge it to 100% and soon after being removed from the charger, it goes to 80% kind of thing.

It's still considerably higher than the stock sad 3400 battery.

btw i cannot test or use the old battery anymore. since the test in January i left it unused in storage and when i had a look at it today i noticed that the battery has gotten out of shape. the profile of a smartphone battery is flat like a popsicle and it was like that in January. now the profile is arched, apparently from some pressure buildup inside, ballooning. the balloon deformation is not too severe but for sure the battery doesn't fit in the phone nor in the Samsung cradle charger anymore.

i'll dispose of it soon.

sum ting was wlong with it anyway: neither mc3k nor the cradle charger managed to charge it to 4.35V, and the discharge curve looked totally different between B800BE and B800BC. good riddance. performed like a fake battery

EDIT: 3rd battery:
1h47min30s for charging in QC3.0 port of BlitzWolf S7
1h44min50s for charging in fake Samsung wall charger

@kreisl Thanks for sharing the interesting data. Given your definition of a joyful charger, it must have been quite painful seeing a rats nest of wires adulterating your DreamCharger. My sympathies. Maybe the next version will include Pogo pins, to help maximize squirrel joy.

Theese will declutter your setup a bit: http://www.ebay.com/itm/261070585341?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT
I bought them and they work flawless.

If you want a more stable setup buy one of theese http://www.ebay.com/itm/360-Degree-...hash=item51df21449b:m:mCyqn9eq1HBsL4vg7Pj5LPg and rip out the guts, and bam you have a true universal charhing dock

etc said:

Very cool. FYI, ZeroLemon makes extended cells for smart phones that have removable batteries. In the realm of 8000-9000 mAh, I have one for LG Optimus G Pro and it's very nice. Triples your runtime.

I've had it for 6+ months and it's beginning to get tired after daily charge cycles, loses capacity. You charge it to 100% and soon after being removed from the charger, it goes to 80% kind of thing.

It's still considerably higher than the stock sad 3400 battery.

Click to expand...

Did you try to let the battery run down? I have to do this time to time on mine. Dont really need to completely run it down but if you are regularly doing this I suppose its cycle life is used up.z

kreisl said:

btw i cannot test or use the old battery anymore. since the test in January i left it unused in storage and when i had a look at it today i noticed that the battery has gotten out of shape. the profile of a smartphone battery is flat like a popsicle and it was like that in January. now the profile is arched, apparently from some pressure buildup inside, ballooning. the balloon deformation is not too severe but for sure the battery doesn't fit in the phone nor in the Samsung cradle charger anymore.

i'll dispose of it soon.

sum ting was wlong with it anyway: neither mc3k nor the cradle charger managed to charge it to 4.35V, and the discharge curve looked totally different between B800BE and B800BC. good riddance. performed like a fake battery

Click to expand...

woah. same has happened now with that 'New/Unused' battery, the B800BE from the OP. the battery has adopted a bulged shape and my phone doesn't work properly anymore, probably due to the battery defect. I have no reasons to not doubt that the B800BE was not a 100% original Samsung battery (what?? ). since the OP, i made good use of it, in the past 3 months i recharged it from 1% back to 100% every night and the USB meter measured ~2400mAh charge capacity last week, and only ~1600mAh this week wtf. A sudden drop of charge capacity, a good hint that the battery was somehow cr*pping out on me. And today i noticed the bulged shape!

The OP was in January. Now we have June. Not even 5.0 months have passed and the B800BE has become yet unusable. It served me very well during that time, i did abuse it a bit a few times with high current charging (2 amps) and high current discharging (recording a high res video until battery was depleted), and now it is bulged that i wouldn't dare to analyze it with the OP technique. Of course i am curious what its discharge curve would look like now.

But analyzing a bulged battery ...

In any case, i have a new compatible battery on order. Not original Samsung. I should analyze it too, since that's what dis thread is all about. Nice exercise.

Nice way of doing that. I use paper clips and rubber bands, and my clip lead dummy cell is ring terminals screwed onto the ends of a wood dowel.
Yours made me think...a dowel with a slot and two pin contacts on top...it might be doable. I have plenty of old pager chargers with tiny pins and springs...

Alternatively you can scavenge the case and pogo pin connecters from universal phone chargers like those below ($1.61 on eBay).

i was silly enough to do a final cycle on the bulged battery because i was curious about its capacity or performance. what are typical currents in a smartphone? it depends on the apps you're running. maybe 500mA is as high as it would get when shooting a high res video. so that's what dex graphed:



poor battery performance and disappointing. didnt live a long life and it was presumably an original samsung battery!
okay maybe i abused it with 2A charging and such, but i have never seen a bulged samsung 18650 for that matter.
anywho i got a 6.5eur replacement battery, obviously not original since the label does not say samsung. apart from that detail, the new battery looks like a lookalike

i analyzed its capacity with 4 different discharge rates and used the same charge/discharge settings as the ones from the OP. poor results .. as expected from a non original battery, for sure i wouldnt buy it again:



charging looked like this in dex, nothing special i guess:



all 5 graphs put into perspective with excel:



I also checked the charging from 1% to 100% with the USB doctor and got 2078mAh or 2130mAh, so ~2100mAh average. This value is lower than the above graphs because as explained in the OP, the smarphone 1% is at ~3.5V whereas i did the analyzing down to 2.78V cutoff. in any case the 2100mAh result of the USB doctor confirms my mc3k measurements:

it's a poor battery. nominal 3200mAh and there is less than 2500mAh in it (because it is non original samsung) and in effective i can use only 2100mAh of the 2500mAh. tsss.
:sick2:

it's a poor battery. nominal 3200mAh and there is less than 2500mAh in it (because it is non original samsung) and in effective i can use only 2100mAh of the 2500mAh. tsss.
:sick2:

Click to expand...

Methinks thou dost protest too much.

No doubt your original 2A testing and whatnot eventually lowered the batteries life.
A good comparison would be for others who also have this type of cell phone battery to see if they eventually "grow lumps".

the samsung was fun while it lasted. the other month i dropped the phone accidentally on my tiled floor from 2 feet height, the phone landed on its back, but the front screen got damaged, all black.

i looked hard for a 2016 model replacement and realized that pretty much all new models from the Asian manufacturers have built-in batteries: even though it is possible to buy replacement batteries, the batteries are not meant to be replaced. i totally get though WHY new models can't offer user-swappable batteries anymore: the material. Note3 was an all plastic phone: plastic back, plastic frame, plastic inlay. Nowadays phones are all metal, all glass, all ceramic. With such materials it is impossible to offer easy access to the interior because the screen must be sealed with the frame and etc. How could a metal/glass/ceramic phone offer an open-able compartment (also made out of metal/glass/ceramic) for the phone, without ruining the elegant unibody esthetics? Not possible. Phones from budget lines, cheaper Samsung models, will still offer user-replaceable smartphone batteries but premium models or premium material models will sport built-in batteries only.

My new phone, a Non-Samsung Note4, has a built-in 4100mAh battery inside and that's where it stays until it is not usable anymore (in 1.5yrs my estimation). From youtubes i can see that its battery has a tiny clip connector, so it will be impossible to use my above method with the crocodile alligator clips anyway.

My previous post, 3.0 years ago, woah time flies! :sick2: I don't do such systematic tests of smartphone batteries anymore because:

• nowadays the liion battery is built-in in the modern sealed smartphone, with special micro connectors; while professional repair shops could still exchange the built-in battery, it is much rarer for the common user (like myself) to get manual hold of such a modern battery: if i can't exchange the battery myself (you'd need special tools, youtube tutorial, re-sealing tape, and practice/experience), why would i order the replacement part from ebay? i wouldn't. needless to say, whenever i do get my filthy hands on a smartphone battery, i am interested in testing the battery performance, i.e. graphing the discharge curve (as done here again).
• as this thread has proven, it is totally sufficient to use a cheap USB doctor and measure the charging capacity (from "0%" to "100%" phone battery indicator). for a new battery, the charging capacity almost equals the nominal capacity, and it is a consistent reliable method for approximating the actual battery capacity.

A week ago my neighbor bought a new 2019 Huawei phone with built-in battery because his old 2015 ZTE phone with user-exchangeable battery had become a nuisance: after charging, the phone battery indicator would drop from "100%" to "20%" within a few hours in standby mode (so he claimed)! Same observation with either battery sample. At the time of purchase, the phone was supplied with two identical cells, production date 2015-10-20. I labeled them "old" vs "new" for distinction. He wasn't sure which cell was the more used one. But he was sure that both batteries *ucked and that they were the reason, the cause of the phone nuisance.
Was he right?:thinking:

Even though the last time i did such a test was 3 years ago, the steps to producing the Excel graph were clear to me: connect battery with the diy harness to a mc3k slot, fully charge to 4.35V, mouse-press "Start gathering"-button in DEX on the raspi-Linux (operated from my Win7 machine or Android phone), finger-press <Start>-button on mc3k device (DISCHARGE or REFRESH program), repeat for several test runs, and save all test runs in the same 1 single *.OSD-file created by DEX, export select data to 4 separate *.CSV-files, transfer the files from raspi-Linux to Win7 machine (i did it thru Win7-FTP via WiFi), open the *.CSV files with M$ Excel, and do post-processing of the data (*.XLSX, *.PNG).

As the OP has shown (WinXP, PCLS), one does not need a raspi-Linux nor DEX software to log the data coming from the mc3k. But it is so convenient and stable to let the 2.0W raspi do the logging for hours and days, headlessly, instead of your full-blown 400W PC desktop gaming machine. What a glory, i can't get over it:



The internal resistances of the two battery samples were similar (~250 vs ~280mΩ), so were their tested capacities down to 3.30V cut-off! I chose 3.30V instead of 2.75V in order not to put unnecessary stress on the cells. Click on pic for FullHD resolution:


From the above graph i come to the following conclusions (graph interpretation):

1. the 2 batteries do exhibit different performances. the one cell ("old") is better than the other ("new"), consistently so.
2. the difference is marginal. both cells seem to be still good after all, 3.5yrs after production.
3. i mislabeled the samples (the "old" cell seems to be the less abused one).
4. i can't detect noticeable problems or conspicuities in the battery performance. so, if the ZTE phone is performing poorly, then it's prolly not due to the battery!

Well, that was 10525 phun. Now i am crawling back to where i came from.

250-280 mohm is junk.
my new note3 batts were around 30mohm.
phones draw high pulse current and a battery with that high of ir will fall on its face in a phone.
how much resistance is in that setup?
btw i suspect the fake batteries from ebay and amazon used 4.2v cells which is why they bulged so soon.
my original had faded badly and its ir went through the roof but it did not bulge.

snakebite said:

250-280 mohm is junk.

Click to expand...

thanks. ZTE products is junk.

yes the setup (several contact resistances, plus the diy harness) does have additional resistance compared to a normal battery in the mc3k slot. i am sorry, i don't know the value. because of the many electro-mechanical contacts in the setup there is no point in measuring the resistance of the setup (i.e. setup minus battery) with a multimeter and then substract the value from 250mohm, way too challenging mechanically, contact resistance is a beast, the tolerance in any value obtained would be too high, a worthless value, so much sweat and wrecked nerves for obtaining a worthless value, worthless because of the level of uncertainty, i don't want to sweat

how did you measure the 30mohm of your note3 batts? and do you still use a modern smartphone with user-replaceable battery? those have become absolutely rare. the latest Galaxy J and Galaxy A series phones have built-in batteries only. in any case, i converted to Xiaomi, luv the UI (called MIUI 10) with the frequent MIUI OTA-updates (no matter how old the phone is). xiamoi batteries are built-in but that's the case with other phones too.

i used a **** smith esr.
https://www.flippers.com/esrktmtr.html
still have the note3 but currently on a note8.

This post (#18) refers to post #2 where i had tested a brandnew original genuine authentic factoryfresh Samsung J5 phone battery. Today is over 5.5yrs later and i retested the battery (blue curve). Then i also bought a replacement battery which was advertised on ebay.de as "new original Samsung" (with unknown manufacture date) and tested it too (red curve). I added both graphs to the old chart:

As you can see from the picture, after 5.5yrs of age and use, the capacity has diminished from 2651mAh down to 1761mAh (IR=357mΩ, USB doctor charges "1355mAh", i.e. there is something wrong with the battery and really needed a new replacement).
And to my surprise and dismay, the newly bought (Oct 2021) replacement battery, which looks all identical to the original battery, has a discharge capacity of 2162mAh only 😨 (IR=222mΩ, USB doctor charges "2008mAh"). Moreover i had somewhat of a battery fitment problem, but this could have been a manufacturing tolerance issue after 6yrs of production. However, the discharge curve isn't lying: the ebay "new original Samsung" battery has frikkin poor performance/capacity! Then i looked around on ebay.de, other resellers of the same Samsung battery, and detected several other buyers complaining about poor performance/capacity of the delivered item. I contacted the ebay seller (he is of Turkish/Arab origin?) and he told me that he is "just a reseller". He couldn't answer my questions about the battery manufacturing date and left all other questions unanswered. So I am thinking: if he calls himself "just a reseller", then he won't be able to guarantee that his batteries are indeed genuine authentic original Samsung batteries. Only sellers who directly buy from Samsung factory would be able to guarantee such a thing imho.

At this point i have all the reasons to just believe/assume that the battery unit i got is a fake Samsung battery, even if the seller still believes that it is original. I've got the test result printed out (and i vouch for it), while he has nothing to show against. mc3k displays an internal resistance of IR=222mΩ (that's low for a cumulative resistance) which confirms that i didn't mess up anything in the measurement setup (with mc3k and charging harness and contact resistances) and that the measured capacity is the actual capacity, i.e. with no measurement errors.

So maybe this thread does serve a purpose after all: to warn shoppers that, even if a phone battery is being advertised as "new original Samsung" doesn't mean that it is indeed "genuine authentic original Samsung" or that it performs like one. With old battery models (of the user-exchangeable type), we end consumers are able to verify the discharge capacity quite easily with a battery charger like mc3k. With new battery models (of the built-in type), we can't easily connect them to crocodile/alligator clips, thus i wouldn't know how to connect such a battery to the mc3k:



Popular user-replaceable phone batteries (like Samsung) are convenient, highly available, inexpensive, and easy to test but the problem is that the market is flooded with fakes/counterfeit Samsung batteries. It's become a lottery, no matter how much you trust your reseller: it's not his fault if he ends up reselling counterfeits because merchandise got switched clandestinely somewhere along his supply chain.

Most buyers doht care if a 2600mAh battery comes with 2000mAh only because the ebay battery is cheap (10 bucks shipped) and seems to perform better than the old one (2008mAh > 1355mAh), which is good enough for them. Needless to say, the seller offered me a partial refund and i accepted. (btw the J5 phone is not mine, and it's about time to upgrade to an Android 11 phone 2021 model with 4100mAh capacity cha!!)

Xiaomi.

For my 2016 xiaomi phone with built-in 4100mAh battery, now in 2021, i found plenty of gemani-based ebayDOTde sellers with new unused original(?) xiaomi batteries, distributed by "Sunfavors in Sweden AB" (sealing sticker label). There are several sellers on AliX too who offer the exact battery model, Xiaomi BN41.

Because of the popularity of the 2016 phone, there are plenty of youtube guides on how to replace the battery.

And because of the popularity, it is also good to see sooo many sources from which one could buy the replacement battery (10$/10€ shipped).

The ebayDOTde seller was a geman reseller, obviously. From what i can assume, he receives the merchandise from the Swedish importer and assumes himself that the battery quality is good (and new original genuine authentic factoryfresh unused etc).

I managed to replace the battery but was appalled by how fast the battery status percentage was draining. At 0%, the phone shut itself down and went into locked-out mode. Maybe the phone (operating system MIUI10) has a draining issue but in the locked-out mode any OS-related draining issue would be inactive.

With my Nicjoy USB doctor I measured a full charge: only ~2000mAh went in! (i could have used my EBD-USB instead; when i am bored, i could do that, it'd provide a more precise mAh number) Since we know from this thread that a cheap USB doctor is good enough to measure the charge capacity and that charge capacity isn't much different from discharge capacity, it is safe to say that the "03/2021, 4100mAh" (manuf. date is printed on Xiaomi batteries, nice!) Xiaomi replacement battery has only ~2000mAh usable capacity.

Needless to say, the reseller offered me a partial refund and i accepted. Apart from the gained (negative) experience, i do regret the purchase: i went thru the trouble of replacing the built-in battery, spent/lost money in the process, but didn't gain higher battery capacity (the ~2000mAh usable capacity isn't much more than my old 2016 battery after 5yrs of service, i can tell).

Since i got partial refunds from the ebayDOTde sellers, i could order other new samples of the Samsung and Xiaomi batteries and see if they come closer to the rated capacities (2600mAh Samsung, 4100mAh Xiaomi), but after these two disappointing duds i doht feel encouraged to waste any further efforts. I better buy a new phone instead!

On a different note, when you pull on those tape tabs (built-in batteries are fixed with double-sided adhesive tape stripes which end in pull-tabs), one can accelerate the process of removing the tape stripes by applying a drop of isopropyl alcohol on the tape. Alcohol dissolves the adhesive power of tapes after 3min (as you might know?). Just be careful with the amount of alcohol. Alcohol can also harm the screen/display from the inside. Use "alcohol at your battery" only, if you have serious trouble removing the battery otherwise (bending battery, cracking battery, bending phone parts, etc).

I use the Accubattery app to keep track of my battery. Makes things simple.