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The PC uses a low-power battery to maintain certain information when the power is off; for example, your BIOS settings, the current date and time, and resource assignment for Plug and Play systems. This battery can take one of several forms:

• On many older PCs, it is a large rectangular box that is attached to the motherboard with wires, and often velcroed to the power supply inside the case.
• Some PCs use a battery soldered to the board that looks like a small cylinder or barrel. It is not generally detachable.
• Some PCs use a flat round watch battery in a metal holder.
• Some PCs don't appear to have a battery at all. In this case, the battery may be a lithium type that is within one of the other packages (typically the real-time clock package). It may also be an integrated rechargeable Nickel-Cadmium battery (sometimes called an "accumulator") that is recharged whenever the line power is connected to the machine. These batteries cannot be replaced, although they are rated for a long life (5 to 10 years).

My personal opinion is that having an integrated, life-limited, non-replaceable component like a battery on a motherboard is bad design. There are many, many PCs with perfectly functional motherboards that are more than 5 years old, and having to throw them away over a bad battery is just a waste. Also, if you ever need to clear the CMOS memory on the motherboard due to corruption or a lost password, it is much more difficult to do with an integrated battery unless there is a CMOS clear jumper on the motherboard. For this reason, purchasing a motherboard with a replaceable battery is a very wise idea. Unfortunately, they are getting harder and harder to find.

Next: Jumpers

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