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Laptop Battery rebuild


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Hi everybody,

Reading the article on rebuilding ones own laptop battery pack I have some questions.

I have a Compaq Evo N400c laptop with a 14,4V 2150mAh battery pack. It's label
says it is a 4 cell pack. Some clculations: 14,4V /4cells = 3,6V per cell (which is the industrie standard from what I understand) = perfect !!!

Now, the thing is when the laptop is off the powergrid (which the battery pack only
can keep up for several seconds - maybe 5 or so) A mowning/crackling noise comes
from the battery pack area. It sounds a bit like an old amp which hasn't been
proparly grounded (a sort of 50Hz noise) Even if the laptop is switched off and not plugged in into the mains power it makes this 50Hz type noise.

I assume (so it seems) this noise is produced by the safety electronics or individual cells in the pack. It seems the sound derives from the connector area... No idea what this means...

Before I will attempt the 4 Li-Ion cell replacement I like to know if replacing the cells will rid me of the noise.

Do degraded/broken battery packs make such a noise ussually ? Are the cells
or the safety electronics inside the pack at fault here - Guesstimate ??? Or maybe is the safety electronics damaged or just reacting to broken cells in the pack?

Please advise..

Regards, Sander Tel.


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As a lithium rechargeable battery is used, its running time slowly becomes less and less. It needs to be replaced or rebuilt when its running time becomes too low for you.

Nothing in the protection circuit should make a noise like you have so your protection circuit is probably faulty and replacing the battery cells won't fix anything.

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The problem with laptop batteries is the lithium batteries them-selfs, they don't last that long ask these guys that have delwat hand drills they might get two years of steady use out of them. also there dangerous to rebuild because there welded together and if you get them to hot they blow-up. solder won't work because the heat they generate. best thing to do is just take the bite and buy new ones.

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