Low available storage causes power problems?

I'm currently dancing on the line of where my storage gets so full that it causes my phone to get hot and uses more power than usual.

I fix this by simply freeing up space, like deleting apps and exporting all images and videos.

Currently at 78GB out of 115GB

However, i wasn't as lucky with my previous phone, the X3 NFC, which i assume had the same problem.

But not knowing what i do now, i reached a point where the USB port acted up and didn't charge well, when measured it said 0.1A

it's currently "dead", as it doesn't charge

So, i'm here with a pro that i need to empty once in a while and a drained NFC that won't charge

Questions is:

• What causes this?
• Can i prevent this from happening?

--But mostly--

• Can i charge a phone without using the USB-C port?
• Or at least retreaving anything from a "dead" phone's memory?