It's not a speculation but a fact - sooner or later your shiny new Samsung battery will start showing signs of aging and reduced performance. It's also a fact that some of us wants to keep S5 slim without extra thickness or weight of the extended battery, and would rather prefer to have a spare one they can charge externally and swap when necessary. Either way, a number of S5 owners will be looking for a replacement OEM battery and that's where the nightmare begins. You can cross out most of the cheap ebay or other on-line retailers, especially those claiming 2x capacity in the same footprint as OEM battery - those are all marketing tricks where often you won't even get the original capacity. Going on Amazon used to be a safe choice, but not anymore. The same ebay sellers list their junk under the brand names and people don't bother to check when looking for a bargain price.
But have no fear, there are still a few trusted vendors left to buy your batteries from. Do your homework when you search for replacement batteries on Amazon, look at the vendors who have been in business for at least 2-3 years, offer 12-18 months warranty and replacement, and have at least a few hundred or better yet a few thousand positive feedback comments. I know some lost their trust in review comments because a lot of companies send out free review samples, but you have to be realistic when you see a few thousand 5 or 4 star comments - a company would go out of business if they have to give out that many samples for free So like I said, do the homework but if you want me to save you some time, check out the latest Anker replacement battery for Galaxy S5.
There is nothing really to comment about packaging since it's very slim with a plastic tray and battery and user manual inside. One thing I liked about it, Anker shrink wrapped the battery. I know it was a PITA to remove the wrapping, something for them to consider in a future with some pull out tab, but it felt very secure without worrying about battery contacts touching anything. User manual is self explanatory; this is a battery that doesn't require a rocket science degree
Putting Samsung original battery next to Anker reveals an identical outline shape in length, width, and thickness. Everything aligns with the same contact spacing, the same capacity and NFC functionality, and the same fitment. The only difference was a water tamper seal sticker on Samsung which is not present on Anker. Regarding the performance, out of the box I didn't see any difference in comparison to a stock battery. Granted our S5 phone is relatively new so it's expected. If this would have been a year old Sammy battery, I probably would have seen an improvement from a fresh Anker battery.
Overall, this battery is not about double capacity or some new extraordinary functionality. This is a battery from a highly trusted company that earned its reputation with thousands of 5-star comments/reviews on Amazon over the last 3+ years and probably #1 most popular battery brand (both internal and external) in there. I'm not hyping it up, just stating the obvious by searching on Amazon as well as forums in our community. Anker actually has a really good quality control, a great tech support, a very reasonable competitive pricing, and 18-months hassle free warranty. Like I mentioned before, there is a handful of trusted battery companies and I put Anker at the top as the most recommended one.
Here are the pictures.