Batteries won't charge

I have two IDX V mount batteries both won't charge, The IDX charger will show a solid red indicator, according to the manual it means it detecting and conditioning the battery, after a few minutes the charging fan stops and the light still red. If Idisconnect the battery the light goes off obviousely but reconnect the battery the light wont come back on. Powering off and on the charger goes back to solid red light again. Both batteries has not been charged for about 2 years, they havent been used much but are over 7 years old. Any clue, is the batteries dead? How will revive the batteries? Will using a D-tap charger helps?

Likely the battery is dead. I usually keep some charge to my v-mount batteries every 3-4 months and joined in a while, give it a full charge and use it, whether on a lighting system or camera. But 2 years discharge on a 7 year old battery is probably the culprit. One thing is that if you have just a brick charger, try charging with it. It might take a long time (about 8 hrs) but it is cheap if you don’t have one already and will have you determine if it is the battery or your IDX charger.

Some batteries have a built-in protection circuit that may prevent charging if they have been unused for an extended period. Try performing a reset on the batteries by fully discharging them (if possible) and then attempting to charge them again.

I'd start with @gillrich's idea - do you have a way to fully discharge them like using them in something until they die? That may reset the protection circuit. Then try charging with a simpler charger like the brick style one @Ellory mentioned. Hopefully a slow full charge will bring them back to life. It's worth a shot before declaring them dead.