I accidentally left my iPad plugged in for charging for 10 hours ? Is my iPad battery damaged now?

Definitely not!

All rechargeable Lithium-ion batteries and circuitry, in all mobile electronics devices, are all designed to prevent any overcharging and the battery raye of charge is always regulated to a charge rate that does not overheat the internal baterry.

Your iPad is OK.

Best of Luck to You!

An otherwise heathy iPad will suffer no harm in being connected to external power and/or charging for extended periods - whether in use or not. This usage model is common in Point of Sale and Kiosk applications. The iPad will optimally charge your iPad battery, modifying its charging strategy as appropriate to reduce potential chemical aging.

More information about iPad’s battery management can be found here:

About iPad and iPhone Charge Management Feature – Apple Support