How much could a kindle fire's battery last
You can extend the life of its battery by allowing it to run down to below 50% before you charge it, and by always being sure to charge it fully--to 100%--before using it again.
Till it dies.
There is no definite time of which a Kindle fire can last. It can last until the time it dies. However, the time it dies or the time it will last depends on the usage.
How "much" can it last?