My sister recently bought a 'Genuine Apple' Macbook battery off the online auction store 'TradeMe.co.nz' only to find when it arrived that it was not so 'genuine' after all...
Luckily she will get a full refund for the purchase when she sends the product back, but was informed it couldn't be a fake because 'that was illegal.' However - having the old no-longer-working battery that came with the computer to compare, the differences, while subtle, become apparent. I kind of find it interesting how closely they can match the original... and where they cut corners (or not - see below) on the manufacture.
In the fake, you can see the grey shapes of the apple logo and text slightly overlapping the engraved areas, like black ink printed over colour in a newspaper. You can also see subtle differences in the font used like the 'D' in 'Designed by Apple' or the 'Hg' in brackets at the end, appearing more 'squashed' in the fake compared with the original. The quality of the metal can also be seen in these pictures, with a brushed highly reflective metal used in the real battery, and a more matt, less textured metal in the fake.
Also suspicious is the use of parts in a 'new' product that appear to have marks and smudges from prior use.
Probably the most obvious sign that something was wrong was that the battery didn't actually fit in the computer - it was getting caught on its edge. Maybe it would have fit if I had forced it but - I didn't try my chances. The cause of this difference is because the fake didn't bother to curve the edges of the casing as much as the real one, as can be seen below, leaving a sharper looking edge on the fake.
I think it's a testament to Apple's engineering that such a subtle difference could be so noticeable (though not noticeable enough if they are still making them? Strange when even the test battery at the mac store when investigating the old battery slipped in perfectly, unlike this replica). I don't like to think about what might be inside.