Can an 8AA - battery with a 5v connector be used to power BOTH Pi and UNO?

The Arduino is being powered through a USB cable for serial communication purposes. I have an LCD shield ontop that blocks all pins, so no communication through any pins is possible. I have purchased an 8AA battery holder, which I plan on soldering to a switch so I can easily turn the controllers on and off when done.

If there is 8 batteries in the holder --> 12V max.

I purchased this to lower the voltage to the Pi's maximum 5V.

I plan on attaching the +5 wire to the 5V rail pin on the Pi.

It seems that this method can power them both, but is there going to be a big hit performance-wise?

You need to estimate the total current consumption of your project , or measure with a multimeter, then calculate how long you think the battery will last from its Ah capacity

It’s hard to guess from here , as it depends on what is connected, which boards, whether any power saving schemes are used and so on;but I’d say AA are too small .
Unless you need it , it’s pointless creating 12v , then cutting it back down .

hammy:
You need to estimate the total current consumption of your project , or measure with a multimeter, then calculate how long you think the battery will last from its Ah capacity

It’s hard to guess from here , as it depends on what is connected, which boards, whether any power saving schemes are used and so on;but I’d say AA are too small .
Unless you need it , it’s pointless creating 12v , then cutting it back down .

It won't need to be turned on for more than a few minutes. Worst case scenario, I can also power the arduino with a secondary battery case.