Does it drop very very fast? Does it auto shut down before it reach 0%? If it does, it gone case liao.
Wad phone are you using? If the battery is not removable, try a factory 1st to eliminate any software issue caused by rogue apps. If this doesn't solve the problem, most likely is battery dying.Left it overnight to charge, stopped at 92%.
This morning used and dropped until 15%. Plugged in to recharge 3 hours still stuck at 38%.
Means battery is spoilt and time to change phone?
Used for 1 year 3 months.
Use for 30 minutes web browsing can drop 30%. (average) So dropping about 1% per minute. Use for 90 minutes (screen on) can drop from 100% to 0%. Confirm can't last half a day.
Need to charge twice a day.

Left it overnight to charge, stopped at 92%.
This morning used and dropped until 15%. Plugged in to recharge 3 hours still stuck at 38%.
Means battery is spoilt and time to change phone?
Used for 1 year 3 months.
Oh did not know about this always let it run low before charging, shall take note thanksPossible charger issue..
Worst case is to do factory reset to see if it resolved issue due to firmware corrupted.
Usually to charge until the lightning icon in the battery icon disappear completely which indicated as fully charged.
Then do either power off or restart the phone.
Never let the battery level to down below 20%, as best to charge when battery level is around 30 - 45 % left.
i suspect so cos it ever happened to my samsung galaxy tabi think the battery spoilt. time to change or change mobile.
what mobile is that?