Why do you guys keep operating on the assumption that replacement batteries for cell phones that came with sealed in batteries (i.e. essentially all phones manufactured for western markets in the last decade, or so) are actually available? I understand that this perverse business model of selling almost exclusively premium-only products that turn into useless paper weights after ~2 years invariably leads to a desperate hope in the purchaser, which makes them more susceptible to fall for scams that profit from desperation, uncertainty, and the magical thinking that makes up the gap (even I, being aware of the simple facts I'm about to point out, nevertheless fell victim to what of course had to be a cell phone replacement battery scam -- because they all are, to varying degrees, scams; I'll elaborate on that below).
Here are some basic facts:
1. The claim that cell phones would be bulkier if they had replaceable battery is an egregious lie. Look up the dimensions of the last western Android device whose battery was replaceable, the LG V20. It was neither any thicker, nor did it come with a battery with substantially lower capacity than its peers at the time.
2. The claim that a replaceable battery limits the functionality of the phone is dubious at best. Around the time the V20 was still produced, the recent fad was "water proof" cell phones. Except, as I recall, they turned out not so water proof after all. "Water proof" in the end turned out to mean little more than "could be splashed with water, like when taking a shower). And if you read all the restrictions in the EULA on where exactly you were allowed to use the phone without losing warranty, the "water resistant" feature in reality was nothing of the sort. I don''t recall any other similar claims regarding other features that would be severely hampered by a removable battery door, so I'll leave it at this.
Now, to get to the availability of batteries: this may come as a surprise, but manufacturing LiPo batteries is not so trivial (in terms of barrier to entry) that you have all these previously unheard-of (in reality, fly-by-night -- and I'll get to that in a bit) companies that magically produce exact replacements for popular phone models. In fact, phone manufacturers rely on two sources for their batteries:
1. In-house: this is the case with Sony/Samsung/LG/etc. They manufacture both the phones and another division makes the batteries.
2. Contracted manufacturers: This was the case for at least the Huawei made Nexus 6P, where the battery maker was a different entity that was contracted by Huawei to produce the batteries they used in the 6P.
-In the first case, the manufacturers make their own batteries -- for phones that aren't expected to have their batteries replaced. For warranty related issues, they simply issue a new phone and program the existing IMEI into it, making it indistinguishable from the failed device. Salaries in every part of the world have risen, even while the cost of producing electronics monotonically fell at the same time. There was a point in the past where the two lines crossed and it became unprofitable to repair devices, rather than simply replace them and throw the defective device in the trash.
-In the second case, the manufacturer is contractually forbidden from independently making and selling batteries. The extra profit to them is nothing compared to the loss of profit incurred by manufacturers if their planned obsolescence schemes were foiled by a third party, so this exclusivity requirements forms the basis of any such contract.
What the above effectively means is this: one battery per phone. One digitizer per phone. One...of each component in each shell, as well as the shell itself, for each phone. In other words, the idea that there are warehouses full of OEM parts is a remnant of the (relatively recent, thus the misconception) past. Let me be as crystal clear as I can be: when you are buying a so-called OEM component for any device today, what you are receiving -- irrespective of what the seller claims -- is very nearly always a part that was removed from another existing phone that had been in use for X hours before it was scrapped and gutted for parts (*) (and when I say very nearly, this is simply to accommodate the sporadic exceptions to this hard rule that exist; of course, if you brought this up with any distributor, they would insist that all their products are magically exempt from this universal fact).
(*) To put it plainly: when you buy a "replacement battery" for your phone, you are buying an OEM component that may have optionally been rewrapped to make it seem like someone else manufactured it. To that, I have to say: please provide sufficient documentation (photos, public records, etc.) to prove "Polarcell" (or Green Battery, et al.) has the resources / manufacturing capabilities to make their own LiPo batteries. When invariably it becomes clear that they don't and "outsource" manufacture, then show me the same records for this imaginary, benevolent, hidden giant that's cool with routinely breaking major order contracts that could instantly turn them into the "persona non grata" of the industry (does "you'll live out the rest of your days in a pain amplifier!" ring a bell with anyone?).
Now, to finally cover the seemingly most baffling aspect of the replacement LiPo aftermarket: the fact that there is so much variance from user to user -- that, indeed, not every satisfied real review is a swindle. When you think about it, the reason is quite obvious and follows from the aforementioned facts: because the replacement battery was taken from another device (i.e. in a used state), the actual wear and tear varies widely and to my knowledge there are only two factors that can help in roughly estimating the likelihood of receiving a near-perfect battery on one hand, vs an utter dud on the other (and one factor merely builds on the worst case scenario of the other):
1. How long has that particular phone model been on the market? Chances are, if it's only been a few months, then the batteries sold come from devices that were smashed, or otherwise rendered inoperable. This means there's a good chance that the battery hasn't gone through too many charge cycles and therefore retains a decent amount of capacity. You could even bank on this knowledge, buy up all batteries at the beginning the moment they start appearing, and later gain an excellent reputation as a seller of quality batteries (yes, LiPo batteries lose capacity even when not in use; OTOH, my Nexus 9 was used for 10 days in December 2015 (before I dropped it and smashed the screen) and remained dormant until the end of last summer. Its battery capacity was 17% when I powered it back up and the AccuBattery app shows remaining capacity to be within 90% of OEM/new rating). Conversely, you could buy them for yourself and keep them for later.
2. If the phone came out some time ago, how much time has gone by since production ended? Because all "replacement batteries" were previously used in existing devices, this helps establish the likelihood that you may still come across a replacement that has seen little use. If it's been years since production ended, it means the probability that any battery you buy has decent remaining charge is very low. But keep in mind: as with anything else involving stochastic math, this means only that the mean remaining capacity of the replacements being sold is low -- not that all of them are. Due to the high number of batteries in circulation, you can apply the central limit theorem of probability theory to establish that the probability function regarding capacity of the replacements forms a Gaussian (bell curve): the vast majority are near the mean, but there are extreme outliers as well (but in diminishingly small quantity). So if you consider yourself blessed by Gaia, you can test this out by ordering a replacement under such circumstances.
As for the rest of us mere mortals: so knowing all this, how badly did I personally get burned? Let's just say, I ordered a replacement for my Nexus 6P last year or the year before (i.e. past production cessation) -- from a well known website that provides excellent DIY repair documents (I feel for the guy because no corporation will logically ever sponsor him, and because I firmly agree with his philosophy; but I'm still miffed after being cheated and cannot ignore this -- so as a compromise, I won't name names) and ended up with a battery that (by rough estimate) about 50-60% of the remaining capacity of the battery I was replacing. That battery was down roughly 50-60% of original capacity -- so you do the math.