DeusExMe, all batteries, even this, lose some charge even when idle. I always charge when the meter gets down to one bar, and never lost it all yet in six months.
The thing to consider is how much you have read before it does get down to one bar. With Whispernet turned off, you should be able to go about a week, depending upon how much you read, before needing a recharge. I read several hours a day, and still go a week.
If it gets low with only a day or so of use, then call Amazon, and if the battery is defective, they'll replace it with no problem.