Project works from usb but not battery

My LCD display i2c displays fine for first minute then text fades although led light is on and still works
It's an uno with 2 LEDs if I run off 9v battery it has 6.98v left it works for 1 minute but if I connect to usb all works fine I thought usb supplied 5v so battery should be ok it's a standard 9v battery not rechargeable so I'm guessing 400 may is it just battery current and usb is supplying more

The problem is you are not using a serious battery. :cold_sweat:

And you are using the "Vin" or "barrel jack" which is a bad idea to start with.

Perhaps use a USB "Power Bank". :grinning: "

A 9V battery with only 6.98V is nearly dead. And little smoke detector 9V batteries are almost useless even when new.