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Kindle Case Battery Drain

A few months ago I decided to purchase the new third generation Amazon Kindle 3G. One of my favorite qualities of this device was the e-ink display, which uses no power to display an image. This allows the battery to last for extremely long periods of time without needing to be recharged. In addition, to protect my new device, I purchased the lighted leather case made by Amazon specifically for the Kindle.

Unfortunately, the official lighted case ruins the battery life, even when  the light is not in use! Instead of the week of battery life that I had gotten before using a case, I could now only manage a day or two, even with the device turned off and wireless communication fully disabled. At first, I didn’t believe that the case was the problem. I assumed it was due to the indexing of books, a bad battery, or something else. As an engineer, I decided to test my ideas to find the most likely reason for my bad battery life.

I removed all my books to be sure it wasn’t an indexing problem. I tested the battery without a case. The battery went back to normal. I checked the resistance of the light’s power terminals when off. There was no connection at all. Then, I discovered the ;dumpmessages command. This, when typed into the search box on the device, makes the Kindle dump all logs, including battery drain logs to the internal memory where they can be accessed on a computer. Every 10 minutes, the battery capacity in milliamp-hours, the current potential in millivolts, the load in milliamps, and some other information is logged. By leaving my Kindle for an hour both in the case and outside the case, I would get 6 data points for drain in each situation. Finally, I found that the drain actually doubled with the case on!

The drain with no case averaged 39mA while in sleep mode (when the screensaver image is displayed.) With the case, however, the drain averaged 83mA, more than double the original. But why? The wireless connection was turned off, so it couldn’t be a signal problem. There is no connection between the two clips of the case when the light is retracted. The only other possibility that I could see is that the clips are causing an internal short or in some other way are triggering something internally.

Unfortunately, this is as far as I have gotten. I have read people say that these internal connections next to the clip connection point aren’t an issue, but from my tests they do seem to be. I’m still doing more research, but until I find out the problem, I am just going to attempt to get a replacement Kindle, which hopefully will not have this problem. It seems that the official Kindle cases may not be the best choice if battery life and stability are important. Even the non-lighted cases have been causing many problems.

If I can find anything new, I’ll post it here right away.

Edit: I have called Kindle support and they decided to send me a whole new Kindle. Once I get it, I’ll test it again and see what happens.

Edit 2: I received my new Kindle and immediately tested it. It turns out that the Kindle was really the problem. From the way the logs look, the old one wasn’t going into suspend mode properly, as it continued to report power drain information while it was off. In the new device, it only reports total power consumed in suspend once the device is turned back on. In an overnight test with 3G enabled and the Kindle in its case, the battery drained 31mAh and dropped 50mV, and lost only 3% of it’s total capacity, down to 97% remaining.

It seems that this has fixed the problem, but it is still odd that in the original the case doubled the drain. I’m going to continue testing this to see the effect in my new Kindle.

Tags: Amazon, batteries, electronics, Kindle