I charge my 18650 bats externally to 100% but my mod says it at 0%

What type of charger are you using? Good quality batteries i assume? Any decent 18650 comes with some sort of protection circuit. Lots of times if left totally discharged for a period of time this circuit will “kick in” for a lack of a better term. Luckily this can pretty easily be overcome with pretty simple equipment. Check this out https://batteryuniversity.com/learn/arti...

They explain it far better than i could. Then there’s always a chance the cell has just gone bad and isn’t actually taking any charge. Not too likely though if you are getting a correct reading of absolutely 0%. I would check them with a Voltmeter before and after charging. If afterwards they aren’t reading the correct voltage throw them away.

If the batteries are good then more than likely the main board of your mod needs replacing. Shouldn’t be all that hard to find one. Might take forever to ship but most chinese suppliers i’ve dealt with will literally go out and find whatever board you are looking for, especially if they think you may make a large order…

hope that helps…