Quote:
Originally Posted by HarryT
Can one consider a degradation of battery life to be a fault? It is, after all, a natural feature of lithium ion batteries. That's the reason that I personally prefer to buy devices which has a user-replaceable battery.
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It's a good question, to be sure. I suppose it's a matter of degree and extent of effect. In a nutshell, I judged the PRS-500 to be abnormally degenerating (but I wasn't working with full information about the cell quality and system discharge profile).
Yes, LiIon cells degenerate somewhat over their lifetime, but if maintained well they will perform very well over a long lifetime. Many appliances (and their chargers) and standard usage practices abuse the battery and cause a self-fulfilling prophecy of premature cell degeneration.
Case in point: My digital camera battery is now three years old and still lasts forever. I actually have two which I discharge "fully" to equipment battery warning each time and then swap them, charge the depleted one, and take it off the charger immediately when charged. They have not perceptibly lost life.
As a good comparison, I have two laptop battery packs. One I discharge deeply when traveling and then recharge it fully. I use it about a dozen times a year, about the same cycle as the eReader battery. The other battery pack sits in my laptop while I use it at my desk with the adapter/charger plugged in. In the space of a year and a half, the one that's always on the charger has a lifetime of about 15 minutes now. The one that doesn't sit on a charger has 2.5 hrs of its original 3 hr lifetime.
So, in the case of my PRS-500, the capacity had dropped to half in the space of less than a year, with EXTREMELY light use. If you don't leave a LiIon on a charger, and only recharge it a half-dozen times in that year, it should have 75-85% of its original capacity (that's capacity to charge and discharge, not holding a charge for a year!). In the case of my eReader, it had dropped to 50% -- lasting two weeks or less with NO page turns. Plus, as soon as it hit one bar, it would suddenly shut off only a handful of minutes of use later. Both of those are signs of a bad cell degenerating spontaneously and raising its internal resistance significantly.
I judged it to be a poor cell. Now, after reading the reports of other people, and judging by the performance of the crummy refurb they sent me, this degeneration appears to be the rule rather than the exception. Either they use marginal cells, or the quiescent load of the reader is very high (which I've pretty much deduced from the self-discharge), or both.
I'm going to trade this 500 in on a 505 (or maybe a 700 if they institute the trade-in policy for it in the near future). Then when the cell deteriorates in that one, I'm going to replace it myself with a very high-quality cell.
Thanks for your question. I love talking about batteries. I'm even correct some of the time.
- The Inspector