You have identified an iPad5 - this being quite an old model. Assuming that the battery has never been changed, by age alone, your iPad's battery may be reaching the end of its useable lifespan. Rechargeable batteries are consumable components that must eventually be replaced.
Battery replacement - if required - can be arranged via the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP):
Genius Bar Reservation and Apple Support Options - Apple
This avenue provides opportunity to have your iPad properly tested before committing to the cost of a battery replacement.
Alternatively, you can use Apple’s mail-in repair service - for which you can find details and costs here:
iPad Repair & Service - Apple Support
For practical purposes, in lieu of servicing and returning your own iPad, Apple usually exchange the iPad for a renewed/refurbished iPad of the same model and specification. The cost of the exchange is the same as would otherwise be charged for the battery replacement.
If you have an active AppleCare+ plan, the cost of repair is reduced to a small excess/deductible fee.