Tata Pad uses two CR2032 watch batteries.
The batteries have an average life of about 12 months (depending on usage) and are replaceable. You will receive an email at the address you used to register when the batteries are about to run out.
This will allow you to have a durable product, without having to buy a new one when the battery runs out.
N.B: the battery life depends on the use of the device and can range from a minimum of 3 months to a maximum of 14.