I have discussed with Kindle support the battery life issue. I have a Kindle 1.
Long battery life. Leave wireless on and recharge approximately every other day. Turn wireless off and read for a week or more before recharging. Fully recharges in 2 hours.
This is an exaggeration. My battery with wispernet on lasts 1 day. With wispernet off it lasts 2-3 days with it in sleep mode much of that time
Customer support attributes shorter batter life due to the fact that I have a SD memory card in it. Seems they are only guessing.
Kindle sent me a NEW replacement battery and it lasted for 12 hours with wisperrnet on.
Went back to my old battery and I am waiting for them to analyze the information that they downloaded from my Kindle to make a determination of what the problem is.
You can speak to 10 different people in customer support and each one has a different answer and information on how long a battery should last between charges.