Assuming you mean how long the battery will last:
The Kindle Fire HD 10 has a pretty good battery life. According to Amazon, the battery lasts up to 10 hours with mixed use. So, if you're just reading books on your Kindle Fire HD 10, the battery will last even longer.
Of course, your mileage may vary depending on how you use your Kindle Fire HD 10. If you're constantly streaming videos or playing games, the battery will drain more quickly. But, overall, the Kindle Fire HD 10 has a solid battery life.