Hello Lolabe11 - welcome to the forum!
First, you've not provided much information, e.g. which iPad, how long have you owned it, & have you routinely discharged the battery completely? Second, please read This Information and be sure to scroll to the bottom to understand the need to periodically (once a month) to let the battery 'run down' near completely - this will re-calibrate the battery monitor - hope this helps and please post back if you are having other issues?
Thank youIt is normal for the battery to degrade over time, especially eight years. The operating system the old iPad Mini runs will not be able to support the latest versions either. If i had to decide and the part exchange price for a new device was £379, I would go for it. Backing up the device, which is a good idea anyway, is straight forward.
Any timeThank you