This is for the most current Kindle, "A single charge lasts up to four (4) weeks, based on a half hour of reading per day with wireless off and the light setting at 13. Battery life will vary based on light settings, wireless usage. Audible audiobook streaming over Bluetooth will reduce battery life", that is pretty standard across devices. So, 14 continuous hours. I don't know how old your device is, but it will lose some capacity over time.
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