A few years back I bit the bullet and bought noise cancelling headphones. I was
hesitant because it costed way more than the EUR 22 I paid for my (later found to be)
crappy Sennheiser. The reason for buying one were double: I had problems
concentrating in a noisy office, and my wife found an almost 50% discount on
the price asked for the Denon AH-GC20.

I have to say that I loved them since the day I tried. They're not only circumaural,
but the pads are also flat against the head, making a very good sealing, to the
point that I have almost never used the NC. They're Bluetooth, and they also work
with a detachable cable for when the battery is dead.

Which bring us to 2 or 3 years later. The battery stopped charging after only
one year, so they became wired full time since. This means not BT and no NC.
Initially I didn't care too much because I changed the company I work for, and
now I can choose where I work. But now I have meetings at the time I should be
cooking dinner, so I started missing the BT support again.

Showing them to a friend, I accidentally found that the padding is glued to a ring of
plastic that clips to the rest of the headphone. Later, and by chance, I started trying to
disassemble the right one first, because I thought the battery was on the left
one, and I preferred to practice on the simpler one. In fact, the battery resides
on the right one.

After removing the padding I was confronted to what looked like a glue-sealed
structure. But stretching a little the fabric that covers the speakers I found 8 holes. I made small holes
in the fabric and started poking until I saw a T5 head. I removed all 8 screws,
but later found that [only those in the long and short axis of the ellipsoid were
needed](http://dionecanali.hd.free.fr/~mdione/anotherg/Projects/Denon%20AH-GC20/IMG_20191110_160945.jpg). Also, one of the screws was deeper than what an usual T5 bit can reach,
so I had to borrow a T5 screwdriver. Once the 4 screws are gone, the lid with
the logo came off easily.

The next step was to find a battery replacement. The original one is a LiPo 600mAh
one with the number 383450 on it. This can be read as 38x34x5.0mm, which mostly matches
the actual size of the battery. Asking around, I was told that the battery's capacity is
irrelevant, because most changing circuits use voltage as a measure of charge
state, and at worst it would take more time to recharge.

Biting the bullet a second time, I bought [a 800mAh battery](http://dionecanali.hd.free.fr/~mdione/anotherg/Projects/Denon%20AH-GC20/IMG_20191125_101508.jpg) for around EUR 10. It came with
a connector that I planned to use to connect it to the headphones: instead of
soldering, which I'm very bad at to the point I don't have a soldering iron, I
planned to cut the original cables close to the old battery, strip a little the
ends and insert them in the connector.

Life is never simple. The tinny tiny wires are too thin for making good connection
and the insulator is too thick to fit in the holes. At the end I dismantled the
connector, open the receivers a little bit, passed the insulators with the wires
'combed' back, and [cramped the receivers with pliers](http://dionecanali.hd.free.fr/~mdione/anotherg/Projects/Denon%20AH-GC20/IMG_20191125_133612.jpg). To make it officially bad
quality, [I used masking tape to keep them from shorting](http://dionecanali.hd.free.fr/~mdione/anotherg/Projects/Denon%20AH-GC20/IMG_20191125_134018.jpg).

I hesitated before plugging it in because I really fear this lithium stuff.
Changing a battery that is supposed to be replaced is one thing, and playing with
chemical fire 2cm from from your right ear is another. Happily I'm not an idiot
and I properly matched the black wire with the black wire, and the red one with
its peer. [I plugged the USB cable](http://dionecanali.hd.free.fr/~mdione/anotherg/Projects/Denon%20AH-GC20/IMG_20191125_152742.jpg), and around 1h later the thing was full. I
unplugged it, put it on, and turned it on. It greeted me with its 'Waiting for
connection' sound and I smiled. I tried with the computer, it connected and...
music to my ears! Wirelessly! For the first time in 2 years! And for less than
EUR 10, a couple of holes in a piece of fabric I never see, and... a bulging
headphone.

See, batteries have in their specs not only the sizes, but also the error
tolerance, which for these sizes seems tom be around ±0.2-0.3mm. I have the
impression that this is related to the fact that these batteries come wrapped in
some kind of malleable aluminium sheet. In any case, I took the risk and bought a
1mm thicker battery, and it shows. I thought I had some space and I could cut
some plastic for the extra mm, but on second inspection it's not true. I will
have to hunt for a thinner battery soon, but for the moment I'm happy with my
meeting/cooking sessions :)