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Old April 11th 15, 06:01 PM posted to microsoft.public.windowsxp.hardware
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Default Rechargeable CMOS/RTC Battery was a Bad Idea

Found this on searching for the battery in the Gateway Solo 3350:

Ni-MH type. Yep, a rechargeable battery. Couldn't search on the CMOS
battery for the "HP laptop" since that obviously gives no details, like
a model number.

Of course, even an old and weak alkaline CMOS battery will case
corruption of CMOS settings. It's not the chemistry per se that is the
problem. It's letting the CMOS battery get too weak. I replace
alkaline coin cells at about 3-4 years. Since they are also chemical,
NiMH batteries are not eternal so they have to get replaced, too.

NiMH will self-discharge. That means not using them will eventually
leave dead a once fully-charged battery. The low load on a CMOS battery
is not a good application for a NiMH battery, and equally so for any
applicable where idle storage (non-use) is a consideration.

Were these laptops bought new or used by you?

Hi Vanguard,

The HP laptop model is N3390.

Since both laptops had defective main batteries, and I always use the AC
adapter anyway, I removed the rechargeable CMOS batteries. I soldered
wires to the battery contacts, routed the wires into the area of the main
battery (I had removed the contents). In the main battery case(s), I
installed two AA alkaline batteries (HP), two AAA alkaline (Solo).
I added a diode in series with the battery due to the charging circuit.
Note: The voltage drop caused by the diode in series did not reduce
the voltage that much.


The HP N3390 laptop CMOS battery was located below the mother board with
no access to it!!!! You would have to remove the mother board to get to it.
I used a dremel tool since someone in a NG provided a link to an image of the
bottom of the mother board. This allowed me to know where to cut a square
opening at the proper location.


You started a thread about the N3390 a while back.

And the photo of the bottom of the N3390 is
still around. I can see a coin cell in the
photo, but at that resolution, can't make
out whether it's an LR2032 or a CR2032. The
LR2032 would be the rechargeable type. The CR2032
is not rechargeable. And you have to use a
coin cell type, consistent with the circuit
designed around that socket. (Can't replace
an LR2032 with a CR2032, since the diode
configuration in the circuit would be different.)