Hi John,
Sorry to say but it does sound as if the battery is dead like the Norwegian Blue parrot in the Monty Python sketch.
I don't know if the following contact details will still help as the telly tablet was considered end of life in 2021 but you could contact the telly team by emailing them via virginsupport@exertis.co.uk or by phoning them on 01282 858460.
They might have or be able to replace the battery, but in all honesty I wouldn't be too hopeful. Your best bet might be to see what bargains are available to buy on Amazon Prime day (16th and 17th July although they do have deals prior to that)
Did you try holding the power button for around 30 seconds to a minute to see if that sparked the tablet into life?
The following shows how to reset the telly tablet and may also help get it working. Try holding the volume up, home and power buttons at the same time for 10/15 seconds and if there is any power left then you should see an Android robot or the VM logo, Then use the volume down button to scroll down to reboot
(you might have to go through the wipe cache partition process before you get the reboot option which is)
Hold the volume up, home and power buttons at the same time for 10/15 seconds you see an Android robot or the VM logo. Use the volume down button to scroll down to wipe cache partition, then press the power button. When wiping the cache partition is complete use the volume keys to select reboot system now and then press the power button again. The telly tablet should then reboot in working order.