What does an Inverter Cable do in a laptop computer?

I have a compaq evo N400c that will not use any battery, therefore it is no longer a mobile laptop as it always needs to be tethered to an ac outlet with the ac adapter.... this laptop runs sweet on the ac adapter, but once you unplug it it dies in less then five minutes, when a battery (fully charged) is inserted, the icon still says AC Power, and as it does not really recognize the battery, it warns of low battery and shuts down.  Someone is trying to sell me an inverter cable and claims this will solve my problem if I can have someone install it in my laptop.  The cable is $6 and well worth it if in fact it will solve this problem, however, when I ran the problem initially on ee I was told the problem was with charging circuit built into the motherboard.  I have two of these laptops that have this problem and two that work fine with the batteries, so I need to repair two and want to know if this sound like the right fix?
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There is no such thing as an inverter cable for computers. What they may be referring to is converting AC to DC, which is nothing more than your present ac adapter setup.
IF they are suggesting that you use a blocking diode cable to create a dc current from an ac source, stay away!!!!!! This will result in a pulsed dc current NOT suitable for computers at all.
look here:

go down to the paragraph "what size inverter should I use" and you see "computer" listed there.
The battery charging is a very simple curcuit in the laptop, there is only ablack lead,  ground, and a red lead, +12V or +15V DC.  Look carefully at these thin wires, see if they became dislodged, often the wires break at the solder joins.  If you are careful, you can probably resolder the wires and fix problem.

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You have several identical laptops. The broken ones (B) the working ones (W)
Take a charged battery from a W, insert it into B - does it work ? If not, it's nor the charging circuit that is damaged but the battery circuit completely.
Take a B's battery, insert it into a W and charge it - will W run with B's battery for a long time (1 hour) ?
If not, you batteries are damaged, not the charging circuit.

What will you get for 6$ ? Not an Inverter ? Do you have a picture of what you should buy ?
To me this sounds crap as of now.
reyeuroAuthor Commented:
The ground had broken loose and a little solder did the trick....thanks
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