Lithium ion battery life

[Mike Watterson]

A Lithium might last in an eink ereader for nearly ten years and die with age. You might be lucky to get 2 years from a phone battery if you have to fully charge every day. About 10 use/charges of about 1/10th capacity counts the same as one complete charge cycle. They are good for 600 to 1200 equivalent full cycles. Operation between about 1/3rd and 2/3rds, or maybe 1/4 and 3/4 is about the longest life. They deteriorate with cycles, time and raised temperature. An eink based ereader could be used for hours every day and still need charged less often than a week, even using the same cell as a phone. The screen only takes power when you turn the page, so the CPU is in semi sleep waiting for a button press or a swipe/tap. You can't even turn an Amazon Kindle actually off, only blank the screen, so they need checked once a month or so if not being used, or they run the cell down. The Kobo and some other brands can be really turned off and can be rebooted even 6 months later. Amazon no doubt thinks why would someone buy one and not read at least once a week? WiFi runs ereader's cell down fast, though some firmwares "sleep" the WiFi if it's not being used.
Turn off Bluetooth, Wifi, Mobile Data when they are not being used. Dim screen. Then phone cell life can double. Tablets are harder on cells. Especially the x86 family ones used for Windows as they are poor at poor saving compared to iOS and Android on ARM. A 10" tablet might have two cells. A 7" tablet might be 50% internal area for the cell.

The lithium cells lose capacity with age and with the number of cycles.