My iPad shows battery empty when almost fully charged

As described, your iPad battery exhibits symptoms of having reached the end of its useable lifespan. All rechargeable batteries are consumable items that will eventually cease to hold adequate charge to operate the host device.

The tags appended to your post suggest that you have an iPad with iOS9 installed. Assuming this information to be correct, this would indicate that you have an iPad2, iPad3 or iPad mini1 - all of which are very old models and obsolete. Hardware and battery service for these models ended many years ago.

While you may be able to find a third-party repairer to change the battery, be aware that battery replacement will result in complete reset of the device - losing all installed Apps and data. While you may be able to restore data from a backup, this will not be the case for installed Apps. All 32-bit Apps, compatible with the iPad1-4 and mini1, have been retired from the Apple App Store - and now cannot be downloaded and installed.

If you have one of the listed models, you would be best advised to consider replacement with a much newer model. Of current models, even the entry-level iPad9 has specifications and capabilities that will massively outperform you current iPad - and is compatible with the vast majority of current Apps. Other models are more powerful still.