I've had a FiiO E7 headphone amp for a few years and it's recently gained a new lease of life -- as an audio interface for my LG G3! Sadly, the has G3 shockingly bad audio quality from its onboard 3.5 mm output - riddled with noise, fuzz/hiss and audible aliasing and distortion. This is likely due to poor design from LG in an effort to power save, combined with a latent bug in Android relating to how it scales audio samples, the latter sounding like it's aliasing audio in a certain range of gain due to it internally resampling or something stupid like that. My old Galaxy S3 LTE running Cyanogenmod 10 (4.2.2) sounded amazing, I wish it hadn't died!
ANYWAY! Recent builds of Android (I'm running 5.1) include a provision for audio-via-USB, enabled by default on most devices, so hooking up a micro-to-mini USB cable between the phone and the E7 gives you blissfully great audio quality.
So, I dug mine out of a cupboard - with a flat battery, of course - and charged it up. Soon after, the battery got fat and decided to push the front of the screen out... Ok, time to replace the battery!
As Tek Syndicate documented, it's pretty darn easy to do this, and they recommended also fitting a JST connector to simplify future battery swaps. And if that wasn't easy enough, they even recommended some SparkFun components (a 1000 mAh LiPo cell, and the 2 mm JST connector!) to purchase.
So, some sleuthing later - and it was surprisingly hard to find the JST connector with any of SparkFun's UK distributors - I had my components delivered from Kirkcaldy-based Proto-PIC. I photographed the installation (novice soldering skills and everything!)...
Although the replacement battery is noticeably smaller than the original (even taking into account the swell of the old cell), it's still a snug fit. With some appropriate cable routing, it sits snugly in the space over the components - no adhesive velcro or double-sided sticky tape required, though I might use some just to stop it shimmying by tiny amounts (which it would only do if you shook it).
All in all, really easy to do, even if you only have beginner soldering skills. Proto-PIC came through quickly, shipped the items thoughtfully packaged in a plastic tub... And ended up being pretty much the cheapest supplier of all I researched.
They also had that magical JST connector in stock, so there was no contest. All other UK SparkFun distributors sadly were out of stock - the next quickest shipping quote I had was that it'd be ordered on the 19th with their other SparkFun orders, then shipped from the US...!
Kudos also to FiiO who really sensibly designed their unit with small Allen key screws holding the backplate on, and a really neatly designed and configured circuit. I look forward to many more years of happy listening 🙂