Dell self-test: don't confuse charge level with health (capacity)
... it is new, had a bar led that show the state of the pack and all leds still go on when you press the button
That self-test does not imply that the battery is new. Rather, it implies only that the battery is charged to approximately 80-100% of its
current capacity. For a highly worn battery, the current capacity might be much less than the original (design) capacity. To infer some information about the current capacity you need to perform what Dell calls a
health test. To do so, press
and hold-pressed the self-test button for at least 6 seconds. During the first 3 seconds the number of LEDs that light indicate the current charge level (20% for each LED). After 3 seconds the lights will turn off then turn on again to display the health.
According to Dell "if no lights appear, the battery is in good condition and approximately more than 80% of its original charge capacity remains. Each light represents incremental degradation. If five lights appear, approximately less than 60% of the charge capacity remains, and you should consider replacing the battery".
Note that if no lights come on in the first 3 seconds then the battery may be drained so low that it does not have enough power to run the self-test. In this case no lights come on in the health test either, but this does not mean it is in best possible health. Rather, it simply means that the test did not run for lack of power to do so. Hence if no lights come on then the self-test is inconclusive.
This might not apply to your battery given that it is a clone. Some of them do not implement the health test, or do so very poorly.
Beware when buying batteries on eBay that many sellers (both individuals and companies) frequently confuse the charge test (first half) with the health test (second half). As a result many batteries are mistakenly listed as new or full-capacity simply because they are fully-charged (to
current capacity, however low that might be).
