Member Avatar for phoenix75

I'm trying to get a friends compaq presario to work and had a question I hope someone can answer.

The only way the bios and config data is retained in the system is to keep the ac adaptor plugged in. When the unit is unplugged the config data resets itself to boot from the floppy drive. If I change it to boot from the hard drive, and leave the unit plugged in, the pc works fine. Once it is unplugged, though, it again loses it's config setup.

So, my question is: Is this just a battery problem? Can I replace the laptop battery to fix this problem or does it have a cmos battery that I have to open the unit to replace. Thanks for your help. I hope this made sense.

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As described and as suggested, this behavior almost always points to a failed CMOS (BIOS) backup cell on the motherboard rather than the main removable laptop battery. Replacing the main pack is unlikely to cure loss of BIOS settings when the machine is unplugged. The correct first step is to locate and test the small coin-cell or two-wire CMOS pack and replace it if its voltage is low.

How to proceed safely: power down, remove AC and the main battery, then open the appropriate access panel (check the Presario 700 service manual before forcing anything). Locate the CMOS cell (either in a holder or a small battery pack with a two-pin plug). Measure its voltage with a multimeter — a healthy cell reads about 3.0 V; under ~2.5 V it should be replaced. If the battery is a plug-in pack you can swap it without soldering; if it is soldered to the board, either have a technician replace it or use a qualified soldering repair.

After replacement, enter BIOS, set the correct time and boot order, save, and then verify the settings persist with AC and main battery removed. If a new CMOS cell does not fix the problem, consider a failing BIOS/CMOS circuit or motherboard fault (service manual checks, BIOS updates, or professional diagnosis may be needed).

Safety notes: always remove power and main battery before opening the case, use basic ESD precautions, and match the replacement battery type. For background on the role of the tiny battery see CMOS battery.

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Member Avatar for phoenix75

anyone seen this before?

Member Avatar for sittas87

Hey there
You should Swop out your buddy's cmos with a know good one

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