I have used both STK and Wasabi batteries for many years starting with my old Rebels and continuing through the newer 5, 6, and 7-series; currently I have about a dozen LP-E6 equivalents in regular rotation. Except for my more battery-hungry 7D2, I can typically leave a battery in the camera for weeks between shoots and still get hundreds of shots from it. On a recent tournament shoot, my 6D batteries lasted all week without swapping them out, and the 5D3 batteries easily gave me enough power to capture over 1000 pictures per day with my 70-200 f/2.8 IS.
Not only have I taken tens of thousands of shots with 3rd party LP-E6 type batteries since about 2012, they are all still showing 100% recharge performance on the internal display. The only battery which has yet started to degrade has been a Canon OEM battery, with only a handful of recharge cycles on it. I generally try to leave at least 20-40% charge on a battery when swapping it out, and top them off right before the next time I plan to use them; along with keeping them cool, this is supposed to lengthen the life of these rechargeables.
A real concern, however, is that due to the huge profit margin, people are counterfeiting Canon batteries and selling them through retailers who don't always know they're fake. From what I've seen, you're more likely to get a poor quality battery in this way than by buying a respected 3rd party unit where quality is consistent. Canon has an educational program on the web to assist consumers in detecting these counterfeits, because they are surprisingly common. Bottom line: get a STK or Wasabi battery, save 70% in cost, and don't sweat it. Of all the things I worry about during a shoot, lighting and camera settings are the only ones which concern me - other than periodically looking at the battery level for confirmation, they've never been a worry.