The problem with even legit "OEM" batteries is that many sold on the secondary market are pulls or (almost as bad) horribly-old stock.
Lithium chemistry batteries degrade with *time* irrespective of use. They also degrade with each cycle. Between the two a "pull" is likely to be either worthless or become so within a few months.
Unfortunately you don't know what you're getting with aftermarket ones either. Some of THOSE are pulls with a different label slapped on them! If they're actual fresh cells then they are usually ok, provided the temperature sensor in them is hooked up and is the correct thermistor so the phone's temp sense circuity works right. But you never know with all the chineesium junk on Spamazon and FleaBay.
The same situation exists in the digital camera world; the LP-E6 Canon batteries are often relabeled pulls and are flat-out garbage. Wasabi makes packs on their own and they've all been good in my experience. They still wear out, but you get a couple of years out of them. Unfortunately Canon got wise to it and in the newer cameras changed the chip they use and started going after third-party manufacturers, so with their newer cameras you can't get third party batteries that will read charge state any more.
It would be nice if all the fraudsters were policied off FleaBay and Spamazon -- people selling pulls without labeling them as USED are committing fraud, but nobody would buy a USED battery for obvious reasons (why is it "used" and for sale unless it's half-dead or worse!) ;-)
I got a few used V20 batteries (one of them a little more worn). It still works fine.. the older and more used battery is weaker. Cool thing is if they advertise it as authentic or brand new and you find out it isn't, they'll refund you and you can keep the battery because it's not worth it for them to pay to ship it back.
Funny thing is a used, authentic LG battery is STILL better than a Chinese knock-off or generic battery.. those batteries are not made according to standards, sometimes even lying about the actual capacity.. could be even dangerous to use.. if you're going to buy a 3rd party battery, make sure the company is reputable. Don't be afraid to buy on Amazon or eBay, honestly sometimes the seller (US based) does not know if the battery is real or not, they just buy them, and they'll give you a refund if you are not happy.
The authentic batteries actually lasts pretty long.. as long as you take care of it (don't let it reach high temps, never let it drop below 15%, take it off the charger when full, give it a break once in a while).
About Canon and manufacturers not allowing 3rd party... there's something called planned obsolescence. Everyone can AGREE that computer printers have some type of planned obsolescence.. in fact they have been through some lawsuits because of it. They do not allow 3rd party ink nor allow you to refill the ink (you used to be able to refill inks at Walgreen's). There's a chip built into HP and Samsung printers that monitors the number of print jobs before activating self destruction (someone found this, look it up yourself). Certain devices are more prone to planned obsolescence, and certain manufactures (usually big names like HP, Apple, etc.). Apple's "battery/slowdown gate" was clear proof of this... Apple is notorious for NOT allowing 3rd party repairs.. especially their computers, causing them to slow or fail after some time... The sooner we can call out these manufactures, the better. Zack from JerryRigEverything is doing a GREAT job letting people know how durable flagship phones are, exposing the ones that have design flaws (Pixel 2 phone failed the bend test). So far, LG has seemed like an honest company, even owning up to their mistakes (replaced or repaired the G4 and V10 for bootloop, gave 2 year warranty on the G6 & V30, not a single bootloop reported since). Smartphone sales are slowing down and manufacturers are freaking out, they will make sure people will buy their phones one way or another.. even if it means designing the phone to last just so long. Say to
#plannedobsolesance and let's not deny the fact.