The size is slightly to big. It was hard to fit.
This is high quality accumulator! Sizes are good (about 1 mm wider, but it's fine). I've replaced 3-year old accumulator of Sony's SBH-50 headset with this one and USB meter indicated a 66% increase of capacity. Operation & full charging time increased almost twice! Definitely recommend as a replacement, just be careful with NFC antenna. As I didn't need protection circuit I simply desoldered it, but during test charge and discharge cycle I've managed to reach as low as 3.3 V and as high as 4,5 V. Seller didn't respond with any corrections. So, I guess, use it at your own risk? Here are some photos of charging this new accumulator inside of the headset.