it is important that battery be removed when flashing using SP Flashtool
but then Xperia C's battery cannot be removed.
For common mtk device with dettachable batteries, the most common steps to flash using SP Flash Tool are:
1. Make sure the usb driver for your mtk devices are installed
2. You have the scatter text file (specific for your phone)
3. The recovery.img that you want to flash
4. DO NOT CONNECT YOUR DEVICE YET
, run the SP FLASH TOOL.
5. Click scatter loading then select your scatter text file
6. After selecting scatter text file, check the box beside RECOVERY then select your recovery.img
7. After selecting your recovery.img, click on download (or F9) - it is important that your phone is not yet connected via usb cable
8. After hitting download, yes press YES when a pop-up message appear (saying not all images ...)
9. After step 8, this is just the moment for you to connect your mtk device without its battery.
Usually the bar with percentage below the SP Flash Tool will turn red, then purple, then yellow (it means that it is flashing perfectly). Just wait for it to complete
10. A green circle will appear when it is successfully flashed.
I hope it helps. Credit goes to the developer of SP Flash Tool.
P.S. - to developers out there, I am quite dumb about this. Will the open source provided by SONY for Xperia C be useful to develop CUSTOM ROM/S? Link provided below: