If you take a lot of pictures.... this is a significant point. DSLRs use very little power to take a picture. Mirrorless require constant power to show something on those screens and view finders all the time--not much different than your smartphone. While the Mirrorless is smaller... you might find your camera bag full of expensive batteries.
Not sure of your bias against mirrorless, lol.. You seem to nitpick and exaggerate any difference you see. It is true that on average, battery life is better in a dSLR.
But that's just on average. It's partially because of the extra screen use, but it's also because most mirrorless have chosen smaller batteries, to help keep down the weight. There are some dSLRs that have about the same, or worse battery life than many mirrorless.
For example, the Sony A6000 is rated for 420 shots. Not great. But the Canon SL1 is rated for only 380 shots. So the mirrorless beats the dSLR by 40 shots.
For the Canon Rebel t6i -- 440 shots.
So in other words, mirrorless has the same battery life as consumer Canon dSLRs.
Nikon uses a larger battery in their consumer dSLRs, increasing the weight, but also giving slightly better battery life.
The Nikon D5500 can get 820 images, compared to the Sony A6000 420 images.
So to match the Nikon, you need 1 extra battery. Not a bag full of expensive batteries.
And that 1 extra battery: There are $10 to $20 third party batteries that will work. First party is $49, and weighs 2 ounces.
Now, poorer battery life on average is definitely something to consider as a con to mirrorless. But it is also a con against Canon as well. It's 1 thing to consider, on a long list. I actually always carry extra batteries -- I carry 1 extra battery for my dSLR, and 1 extra battery for my mirrorless. Unquestionably, I need to re-charge the mirrorless battery more often.
So the poorer battery life is indeed a negative, but a rather minor one. In fact, the related negative that is much bigger in my mind -- The 1 second start-up time.
What I'd suggest to the OP --- If you have a local store that actually has all the options -- (which is getting harder to find), go try all the dSLR and mirrorless that fit into your budget. See how they fit in your hand. See how they feel with using the viewfinder and the LCD. See if you like the control layout. And then pick the one you like the most. I wouldn't get hung up on which camera can give you 450 shots on a battery instead of 420 shots on the battery.. or if it has 13 EV of dynamic range vs 12 EV of dynamic range. In the end, all the cameras will get you nearly identical results. The only features you might want to consider a bit more carefully:
- Sensor size, but I assume all the cameras you will look at, with be APS-C.
- If you care about video, mirrorless is best, Canon is ok, Nikon is worst.
- If you like bracketing shooting, stay away from Nikon entry level cameras.
- If you want to shoot action on a budget, the A6000 with 11 frames per second is far superior to Canon/Nikon entry level options.