There are few sights sadder than a kid with a new robot, truck, talking doll or hand-held poker game that won't play because Mom, Dad or Grandma forgot one simple thing: the batteries.
Sadly, millions of youngsters will be disappointed Christmas morning by this or some other glitch that makes electronic gift-giving a source of parental peril as well as pleasure.
But whether it's a battery-powered toy, a computer, a camera or a new high-def TV, there's still time to make sure it works when the family unwraps it - and you'll spend your day enjoying the gift instead of debugging it.
First things first. Virtually every device or gadget that requires batteries mentions this fact on the box - including the size and number of batteries required. If they're not part of the bundle, a "Batteries not included" warning should be somewhere in the fine print. Look for it.
Check the battery size twice - it's easy to confuse AAs with AAAs, or C's with D's. They're not interchangeable. Be extra careful with radio-controlled cars, planes and other similar gadgets. They often require two sets of batteries in different sizes - one for the controller and one for the car or truck.
Some gadgets will surprise you. Most digital cameras, for example, use proprietary, rechargeable batteries, but a surprising number rely on AA cells.
If your gift camera uses AAs, make sure there's a set of starter batteries inside the box. If not, buy them yourself. Even if there are batteries in the box, an extra set is a good idea, because the cheapo alkalines that camera makers throw in will probably dry up after an hour of shooting.
Disposable lithium batteries are expensive, but they're the best for cameras because they're designed to provide bursts of electricity.
For portable CD players and most other gadgets, alkaline batteries are fine.
Once you've taken a gift battery inventory, consider buying an 8- or 12-pack of each size you need.
When you get over the sticker shock from this exercise, you may decide it's a better to get one or two sets of rechargeable batteries, or several sets in different sizes.
The big battery companies all make chargers that can handle multiple types.
The best overall rechargeable batteries are nickel metal hydride (NiMH) cells, but they're also relatively expensive. Nickel-cadmium (NiCad) batteries are cheaper but don't have as much staying power and require occasional deep-discharging to work efficiently.
Once they figure out how much they're spending on this stuff, parents are often heard to exclaim, "Maybe I should buy stock in a battery company."
On to computers. If you're giving one as a gift, Christmas Day perils abound. The worst scenario is that the PC won't work, in which case you'll spend the holiday on hold with the other 3 million people whose new computers didn't work, either. But there is one advantage to offshore tech support: Christmas isn't that big a deal in Bangalore.
My advice: Sometime over the weekend, when kids are in bed, open the box carefully, hook everything up, turn the computer on and make sure it actually runs. I've seen studies showing that 10 percent of home PCs arrive with at least one faulty component.
You can go as far as you like after that - such as making sure the computer works with your printer or home network. If your gift PC doesn't work out of the box, return it for another one or resolve the problem with the maker's tech support crew before Christmas Day.
That done, pack everything up again and wrap it (if you're into wrapping large boxes). If your spouse or kids want to know why the box looks like it's been opened, tell them you wanted to make sure it worked ahead of time. That way you'll look like a hero instead of a hapless idiot.
Whether you're replacing an old PC or setting this one up in a new location, buy a surge-protected power strip so you'll have enough outlets. If an existing power strip is more than two years old, replace it. Surge suppressors die a little each time they do their job, and after a few years they lose their capacity to protect sensitive equipment.
If Santa's bag includes a new printer, ask him for a ream of paper, too. It's a pain in the neck to scrounge around for scraps. For digital photographers, a pack of 4x6 photo paper is always welcome. Splurge on the printer maker's brand - it will make better photos than cheap generic stuff.
It doesn't hurt to buy a set of ink cartridges either. Most printers come with barely loaded "starter" cartridges that will run out of ink the minute you have something important to print.
HDTV sets are the most problematic high-tech Christmas gifts because most buyers haven't set them up before. In fact, technicians tell me that many customers who think they're getting high-definition images really aren't because (a) they don't have a high-definition tuner box from their cable, satellite or fiber provider, or (b) their HD box isn't hooked up properly.
For this reason, cable companies may insist on having their techs set up HDTV sets, instead of allowing customers to pick up a new set-top box and do it themselves. This requires a service appointment, and by the time you read this, it's probably too late for a set you plan to unwrap on Christmas morning.
You can still hook up a new set, of course, but you won't get HD quality unless you're willing to invest in an antenna - which is what people who don't have cable or satellite use anyway.
For $25 to $50, you can buy a decent set of rabbit ears designed for over-the-air HD reception. You can also try an existing antenna if it includes a loop for the UHF band.
If you're willing to read the manual that comes with the set, you should be able to set things up so you get HD broadcasts, when they're available, directly from local stations. You won't get HD cable stations, but you'll be able to see what the HD fuss is all about.
Have a healthy, happy and bug-free holiday.