Hello friends. I bought the NanoVNA v2 Plus4 Pro from tindie.

After using this for a while, I noticed that this device cannot work without the USB connection.
I thought this had an internal battery and the USB cable can charge this.
*As soon as I unplug the USB cable, the NanoVNA turns off.*

May I ask how to power this without the USB cable?

Also, what is the "E" mark under the calibration letters? Hope that is not an ERROR symbol...

Thank you so much for your help

Hi, depending on the shipping method selected the battery may not be included, you can insert a flat-top unprotected lithium ion cell like the following:

This type of battery can be found in e-cigarette shops.
Thanks

The ‘E’ letter is an indicator that the ‘Enhanced Response’ feature is enabled.   You can find that option on the ‘Calibrate’ menu.   You will notice the letter appears and disappears as you check and uncheck the option.

Do make sure that your battery is seated well.   On my Plus4 unit I have experienced an issue where the unit did not charge or operate from battery due a poor connection.  You may need to clean the battery and holder contacts.  Took me a while to find the sweet spot and multiple insertions and removal before I could get mine to work reliably.