6D just doesn't accept batteries

[darcio2014]

I noticed yesterday that the 6D just doesn't accept batteries that aren't original: it gives an irregular fit alert and shows the battery as empty, even though it's full (which I saw on the 7D that I was about to deliver after the sale). In the 7D the same battery works perfectly. 

[deebatman316]

Are these Genuine Canon LP-E6 series batteries or 3rd party batteries. I would use OEM batteries to see if the camera works correctly.

-Demetrius

Current Gear: EOS 5D Mark IV, EF 16-35mm F/2.8L III USM, EF 24-70mm F/2.8L II USM, EF 50 F/1.8 STM, EF 85mm F/1.8 USM, EF 70-200mm F/2.8L IS III USM, 430EX III-RT, 470EX-AI & 600EX II-RT

Retired Gear: EOS 40D, Sigma 17-50mm F/2.8 EX DC OS HSM & EF 28-135mm F/3.5-5.6 IS USM