I'm obviously very late to the party, and everybody who knows the answer (or was willing to reply) left years ago! Nevertheless, I am very grateful to everyone who created and helped to improve Make_PE3 - it is perfect for my needs.
I sometimes use an external USB3 (and less often an old USB2) external drive plugged into the laptop so, in the early days with Make_PE3, I copied the USB3 drivers into the "C:\Make_PE3\PE3_mod\PE3_add\amd64\Windows\inf" folder and it worked like magic - nothing else to be done. They don't appear in Device Manager in a Virtual Machine, but correctly installed according to Device Manager in a "real" LivePE.
With hindsight, I realise I was misled by how easy it was to add USB3 drivers to the PE; I didn't have to learn anything!
In case someone else like me comes along, I'll describe how I solved my problem, but it will prove how ignorant I am - there is sure to be a much more elegant solution.
My installed OS and the PE source iso is Win7 x64 so the steps below are specific to x64. When creating the PE ISO, I use the first option without using AIK, with Adobe Flash and Net Framework UNticked and the "Min" version selected.
Navigate to the folder: C:\Make_PE3\PE3_mod\PE3_add\amd64\Windows\System32
You can edit the "driver_fix_bs.cmd" if you wish (or any other of the built-in "driver_fix... files), but I want a PE for simple utilities such as Defrag and ChkDsk etc so I chose to create a custom file by opening "driver_fix_bs.cmd" and using File > SaveAs to the same folder - I used my initials in the file name "driver_fix_minMH.cmd" because it has meaning for me. Then I deleted more than half the content - reducing the lines from 92 to 38.
I added the following line:
While learning how to get the battery driver, I also learnt how to pre-install the Standard Enhanced USB2 driver by adding this line:
Navigate to the C:\Make_PE3\PE3_mod\PE3_add\amd64\Windows\SysWOW64 folder and open the "startnet.cmd" file.
If you chose to use the "driver_fix_bs.cmd" file in Step 1 then find and UNcomment the following line by removing the leading :: characters
start "Driver Fix PE3 - Wait ...." /wait "X:\Windows\Sysnative\driver_fix_bs.cmd"
In my case I added the following line
start "Driver Fix PE3 - Wait ...." /wait "X:\Windows\Sysnative\driver_fix_minMH.cmd"
Create the iso in the usual way and test it - hopefully the power icon will automatically be visible in the notification area on the status bar. Check Device Manager if you used the Standard Enhanced USB2 command. Here's a pic of my Device Manager in my latest PE - whippee!