laptop battery puzzle

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On my laptop (ASUS 8400 series), the second Li-ion battery failed after 2
years (the first had lasted 2 1/2 years), so I ordered another. This charged
to 70% at first and then its maximum charge declined by 3% per day down to
0% over 3 weeks. I returned it and was sent another which charged to 56% and
then did the same 3% per day decline. A third battery was sent which charged
to 80% and first but declined like the others. I sent it back when it was
reaching 56%.

The battery charging light would go out when the 'capacity' was reached.

The company tested this third battery and say it charged to 90%, 96% and
100% in three consequtive tests and is not therefore faulty. They are
proposing to refund my money anyway.

My question is - does this behaviour reflect a failing charging circuit on
my laptop or is something else going on? The three recent batteries were
from a company that I have not dealt with before and look like chinese
copies. The first replacement (that lasted 2 years) was  a MrBattery unit
supplied by the notebook supplier. Should I try and get one of these again
or am I likely to be wasting my money? (a battery costs about 30-50% of the
current value of the machine)...

FWIW the behaviour was the same under Linux and Windows.

Any comments appreciated


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