To fix a PC clock problem, get a new system battery

Question: My computer clock is so unreliable that I can set it, and the next day it’s fallen an hour behind. I’ve corrected it a few times in both Windows and DOS. Does it mean it’s time to change the battery in my system? – Vic

Answer: If you’re lucky, yes, it’s a simple battery replacement job. If you’re unlucky, you’re going to have to replace your motherboard.

“These symptoms are not always caused by a dying battery,” said Kirk Reid, a senior support technician at CompuSmart in Edmonton. “Many machines now are using Real Time Clock (RTC) chips instead of a battery.”

Real time clock chips are the most reliable of all the battery solutions on PCs today. They look like a black rectangular chip attached to the motherboard and often have a little picture of a clock face printed on them. If you have one, typically you won’t have to worry about time-related problems ever again because they last up to 10 years (unless, of course, they’re defective).

You can purchase all types of batteries online from

The second most reliable batteries found in systems today are Ni/Cad or nickel/cadmium batteries. “They charge while the system is on,” explains Linda Rohrborough in her IDG book entitled Upgrade Your Own PC. “They can, however, wear out and corrode.”

Some systems use a lithium battery that looks like a small oil drum on the motherboard. Others are coin-shaped units and are either attached with solder or placed in a holder. “Some systems may have a battery pack of three AA or AAA alkaline batteries,” explained Rohrborough in her book, which covers batteries and power supplies at length.

Finally, if you’re looking at your motherboard and you don’t see a battery like the ones above, you might have a proprietary battery system, she adds. Check with your system’s manufacturer or the motherboard manual you received with your system.

If you find that your battery is soldered onto your motherboard, you may get lucky and discover an “external” battery port. Even though this port is inside your machine, it’s classified that way to differentiate between the internal battery which is also attached to the motherboard. Look for a set of three or four pins marked something like: EXT-BAT. In the event that you do have this feature, you’re in luck. The external battery pack costs about $10.

The sticky problem with the “external” battery port is that a jumper might need adjusting so the system knows to switch over to the new battery. If there is no jumper, your system may automatically detect the external battery pack or you may have to enable it in CMOS.

Speaking of CMOS, be sure to record your CMOS settings before switching the battery – failing to do so will leave you with a computer that doesn’t know anything about itself. For more information, check Rohrborough’s book.

For the safest course of action, take it to your computer dealer for a look-see. If you can determine that your machine’s battery is replaceable, the cost should be minimal. If the problem persists, it may be new-motherboard-time.

If the machine is older than one year, go ahead with the battery repair. Worst case is you’re out a little bit of money. If it is newer, your computer warranty should cover it.

If the machine is older and the battery is losing power, you may run the risk of losing your CMOS settings. That’s the part of the computer that remembers crucial information about your system when you power down. Most importantly, your hard-drive settings are stored there.

“If newer machines lose battery power, they can auto-detect hard-drive settings, while an older machine would forget the hard-drive settings,” said Jim Hendy at Edmonton’s Campus Computers. “Usually, on our machines, if a machine is only losing time, it is a symptom of a defective clock chip (RTC) and we will replace the motherboard.” Hendy’s offer of a faulty motherboard replacement should be echoed by most reputable computer dealers.