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The laptop battery for my Compaq Presario CQ40 seems to be broken because it does not charge any more when connected to the mains.

Can this be repaired or I should call it end of life and replace it?

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@sblair Nice edit of title question is now more understandable! – aibk01 Sep 28 '11 at 16:36
How old is the battery? – music2myear Sep 28 '11 at 16:43
@aibk01 Please don't leave comments asking for upvotes. I think it's sometimes ok to remind new users to accept an answer, but not immediately after posting your answer, or within a few minutes of the question being asked. – sblair Sep 28 '11 at 17:56
up vote 0 down vote accepted

Unfortunately, it will need to be replaced.

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Well I think the charging IC might have burnt out Compaq uses TPS 51125 by Texas Instruments for that I think. Also trouble shoot if your charger is ok. When the battery starts getting dead. What actually happens is the voltage decreases than the rated one and there is a surge if current than the rated value. Have you checked that out. A faulty battery usually gets charged except in some cases, however the charging discharging time is less.

So after going through all the issues, still if doesnot work you need to replace the battery. Do get it checked, I saw one or two odd cases when an IC on battery was faulty and was able to be repaired.


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Laptop battery packs are made up from a number of smaller, individual cells and although it is possible to replace them, mixing old and new ones can lead to nasty charge/discharge imbalances (so it's really change all or nothing) and some of the cells are tricky to solder/desolder, plus you will have to crack open the plastic case AND disassemble the unit - and some of them are 'potted' to seal the whole assembly.

I looked into rebuilding a Lithium-Ion battery pack a year or so ago and concluded it was not worth the time, hassle and cost when reputable suppliers benefit from economies of scale.

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It is possible to replace failed battery cells - but not recommended.

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