Check your battery’s health
As mentioned earlier, Lithium-ion batteries degrade over time — or sometimes, earlier than they should. If you’re seeing really low battery life, check the physical health of your battery, so you know whether age has caught up with it, or — if it’s fairly new — whether you need to take a trip to the Genius Bar. On your iOS device, in Settings > Battery, a message should show at the top of the page saying that your battery needs to be serviced, if that’s the case.
This is too vague for us. If you feel the same, try CoconutBattery — a free Mac app (coconut-flavour.com) that tells you the maximum charge your battery can currently hold, and how that compares to when it was new, indicating any deterioration. If you connect an iOS device over USB, it can show the same info for that. It also shows how many charge cycles the battery has been though. Click the + sign to store data, and use the History tab to compare over time.