Faulty new battery for MacBook 13" A1278

Faulty new battery for Macbook 13'' A1278

I bought a new battery from here in order to replace the old one, which was aging. I'm EU citizen.

Unfortunately it suddenly showed signs of malfunction. The charge was very low. Initially I thought it was just a matter of calibration because the battery was new, so I just kept recharging it with the best accuracy.

But after barely 50 cicles the "need assistance" message showed on system profiler. I kept using it in hope of self healing, but it eventually not happened. The battery never went over 1 hour of charge. In the last two months the situation got even worse, with the battery charge lasting for just half an hour, often shutting down my computer without any advice.... sometimes it happens even while charge is showing 100% !

It's really annoying at the point that I almost need to put back the old, aged battery.

The charger is in perfect condition. I bought a brand new original Apple charger months before changing the battery. I think it's just a faulty part and I should send it back. It's covered by warranty.

I bought it from the EU store last December the 28th, 2015. (Order no. EU 107470)

I made a few pictures of Coconut battery status, last June and end of August (now).

- 1st of June 2016: http://i.imgur.com/uvMnVDl.gif

- 28th of August 2016 (won't charge more): http://i.imgur.com/VYGzle4.gif

- Battery requires assistance: http://i.imgur.com/dfGkDLf.gif

By viewing them you can easily check how the situation got worse: doubled the cycles in the last three months! The same amount took six months up to last June since I bought it.

What should I do now to exercise my warranty? Should I send the defective part back or should I send them evidences first, waiting for their request to send them back the part?