Hi reg214
and welcome to thia Apple (user-to-user) Community!
Re: "iPad Face ID and fingerprint recognition not working.Have an Ipad 9th generation
The system won't let me reset ..."
"... a techie says it might be the sensor as Ii had a new battery installed a few weeks ago".
You might want to check that the sensors are quite clean, and that nothing is obstructing them.
or
It could be that Face ID is temporarily disabled or turned off, accidentally or purposefully.
Apple support has a trouble-shooting article online (link below) that may help:
(NB: Article also explains how to reset Face ID and set it up again.)
See what to do: If Face ID isn't working on your iPhone or iPad Pro - Apple Support
Also:
You can see what to do: If Touch ID isn't working on your iPhone or iPad - Apple Support
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Re: Is it worth repairing or is the 9th generation getting obsolete.?
Your iPad can still install the latest iPadOS updates and upgrades so is by no means obsolete as yet.
iPads (like 3rd and 4th gen) that can no longer install recent iOS versions are called "obsolete" by Apple.
According to Apple support's article:
Obtaining service for your Apple product after an expired warranty - Apple Support
"Products are considered obsolete when Apple stopped distributing them for sale more than 7 years ago"
Seems Apple only stopped distributing iPad 9th gen. in 2024.
However, if you consider purchasing a new iPad,
your 9th. gen iPad could likely be used as an Apple Trade In - Apple
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If you still need help:
Wondering if it was the iPad itself, or the Face ID and Touch ID settings you tried unsuccessfully to reset.
Eg:A factory restore erases the information and settings on your iiPad and installs the latest version of iPadOS software. Apple support's online article: (link below) explains how:
Restore your iPhone, iPad, or iPod to factory settings using a computer - Apple Support
All the best :-)