Kindle battery life doubles overnight

When Amazon first launched its latest-generation Kindle e-reader last year, it touted the fact that it could get up to a month's worth of battery life. That same figure is mentioned in a variety of print and television ads.

But after Barnes & Noble launched the new Nook yesterday and played up the Simple Touch Reader's 2 months of battery life (B&N called it the "longest battery life of any eReader"), Amazon countered by magically upping the battery life of the Kindle to two months as the company released a $164 Special Offers version of its Kindle 3G.

So, what gives? Did Amazon actually change the battery in the Kindle?

Well, no. It appears that it just took issue with how its competitor was calculating and presenting its battery life numbers.

Now the product pages for the Kindle WiFi and Kindle 3G (along with their discounted Special Offers counterparts) have been updated with new battery life numbers. "Long battery life - Up to two months," reads the promotional copy. And below that you'll find this paragraph:

A single charge lasts up to two months with wireless off based upon a half-hour of daily reading time. If you read for one hour a day, you will get battery life of up to one month. Keep wireless always on and it lasts for up to 10 days. Battery life will vary based on wireless usage, such as shopping the Kindle Store, Web browsing, and downloading content. In low-coverage areas or in EDGE/GPRS-only coverage, wireless usage will consume battery power more quickly."

I spoke to Michael Serbinis, the CEO of Kobo, which this week announced a new $129.99 touch-screen e-ink reader, the Kobo WiFi Touch Edition. He, too was troubled by Barnes & Noble's battery life claims.

"We didn't calculate our numbers like they [B&N] did," Serbinis said. "If you kept the wireless off and only read for 30 minutes a day, you'd get close to two months of battery life with Kobo's new e-reader, too. But that's not a typical usage scenario."

Kobo currently lists the battery life for its soon-to-be-released Touch Edition at "up to 2 weeks." We suspect that figure may change.

Amazon didn't have any comment about its number changes, but it clearly shows that the competition is intensifying in the dedicated e-reader space and that as these devices become more and more alike, marketing language becomes very significant, especially when it comes to selling points like battery life.

What's disturbing for consumers is that it's actually very difficult to pin down exactly what the battery life numbers are for these types of power-sipping mobile devices because usage patterns and user settings vary from user to user. Also, things like Wi-Fi signal strength could affect battery life.

For its part, in touting that two-month number for the new Nook, Barnes & Noble offers a disclaimer that's similar to Amazon's:

"Battery life depends on device settings, individual usage, and many other factors. Battery tests are conducted using specific units; actual results may vary."

In other words, take all these numbers with a grain of salt. They could change at a moment's notice.

Update: Jamie Iannone, President of Barnes & Noble Digital Products, made the following statement to CNET late Wednesday afternoon (5/25):

With up to two months on a single charge, the all-new Nook has the longest-battery life in the industry and superior battery performance to Kindle 3. In our side-by-side tests, under the exact same conditions, continuous use of the device resulted in more than two times Kindle's battery life. While reading at one page a minute, the all-new Nook battery lasts for 150 hours where the Kindle battery, using the same page-turn rate, lasts for only 56 hours (both with Wi-Fi off). We've also done a continuous page turn test and at one page turn per second, the all-new Nook offers more than 25,000 continuous page turns on a single charge.