MacBook Pro 2011 has faulty power button - How do I enable any key or lid open boot settings?
Opening the lid to turn on a Mac only works if the Mac is asleep/hibernating.  If the power is off, it will need to be turned on.
The reason you have to disconnect the battery is because although your power settings may call for &quot;boot after power failure,&quot; there's never really a power failure if you're battery is connected (and has sufficient charge).
There's two ways you can address this:

Short the power pads.  This is a &quot;stop gap&quot; way to turn on a Mac so that you don't have to disconnect the battery.  Simply bridge the two pads with the blade of a slotted screwdriver or, if you're really daring, solder a wire loop (long enough to come out of the case) with a momentary switch to make it more convenient.  This way, you don't have to keep opening the back cover.  It's a total bodge, but it'll get you by.


Replace the keyboard.  I actually reference this exact keyboard in this question/answer:  Keyboard key stuck or not being recognized; how to fix.  Look under &quot;Replacing Keyboard&quot; in the Answer for specifics.  It's actually very inexpensive.  You may also be able to find the button by itself on eBay.


I advise the latter.  You may be able to get away with only replacing the button rather than the whole keyboard, but either way, it's a better, more reliable fix.