Add info and guide

README.md

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+# Battery Desync Fix NX
+
+
+Battery Desync Fix NX app allows you to calibrate your Fuel Gauge IC with values based on your Switch's calibration data.
+
+
+This fixes issues with battery percentage being wrong.
+
+HOS saves them at power off/reboot and restores them at boot.
+
+The issue is theorized to be hardware bug in Fuel Gauge. It can happen on restore when Fuel Gauge has significantly different values from HOS last boot.
+
+
+## How to calibrate your battery:
+
+You **must** run this app **in succession** to your sysMMC and every emuMMC. Otherwise the moment you switch to another one, it will desync again.
+
+You can start from whichever you want.
+
+Assuming you start with SYS CFW or OFW:
+
+```
+1. Boot SYS CFW
+2. Run the app
+3. Press X button for forcing init
+4. Exit the app properly (press B)
+5. If you want this for OFW, reboot.
+6. Do 2 full charging cycles (??%-> 0%-> 100% -> 0% -> 100%)
+
+- Do not reboot to something else until done!
+- When HOS forces a sleep because battery is too low, wake it again and again until it shows red battery icon.
+- In case HOS powered off, put charger to enter HOS.
+  If it's stuck on black screen and charger icon, unplug/unplug after a bit so you can enter inside.
+  Do not fully charge in there because it HOS will restore the previous Fuel Gauge context.
+
+```
+
+After it's done, you can repeat the procedure for emuMMC.
+
+**Do not switch in-between SYS, EMU and anything else without finishing the 2 charging cycles.** Always be careful when rebooting.
+
+
+## Disclaimer:
+
+No support is provided for that app at all. Use it at your own discretion!
+
+This is app **is not to be included** in packs, etc. It is a specialized app that must only run if user has issues with capacity full and percentage.