What happens to a digital thermometer reading when the battery is old?

April 13, 2020 8:39 AM

Trying to figure out if I've got the rona or hypochondria.

I have two digital oral thermometers, both of which are pretty old - I would say at least over 5 years old. I tried to buy a new thermometer when all this started, but they were all sold out. So I've been taking my temperature with both every morning to get a baseline. They are generally pretty close to each other (within a degree). But my temperature fluctuates wildly when I take them. An hour ago, both were in that over 98.6 but less than 100 gray zone. An hour later, they're both below 98. I hadn't done any activity before the first reading. That they fluctuate in step like this suggests to me that it's my body temperature that's fluctuating. I know body temperature fluctuates throughout the day, but I didn't think it would do it so quickly.

My morning temperature has been consistently low: 96-97. I have a slight fever-y feeling today, but not overwhelmingly so (I know what high fever feels like), and I can be a bit of a hypochondriac. I'm in New York City, so definitely chances for transmission but also for paranoia. I leave my apartment building less than once a week now but I do get a lot of packages and deliveries. I wash my hands, packages themselves, etc.

The only thing this really affects is whether I push myself to be productive today. (I have been relaxing plenty enough, trust me, so really don't want to spend another day binge watching TV when things are piling up.) I'd also like to stop obsessively taking my temperature. Thanks!

posted by unannihilated to Health & Fitness (21 answers total)

I also use a cheap digital thermometer and have been checking in morning and evening. Usually my morning temp is a degree or two lower than my nighttime temp.
posted by sixswitch at 8:46 AM on April 13, 2020

Have you tried replacing the batteries? If they're still giving functional read-outs, it seems like fresh batteries could go a long way in reassuring you. In any case, my experience is that body temperature does fluctuate, whether it's due to normal hormonal changes throughout the day, or activity changes, or even whether I've had something to drink in the last hour.
posted by cocoagirl at 8:52 AM on April 13, 2020

Response by poster: I don't have batteries on hand that fit and since I might have a fever, I don't want to go outside to get them. I don't have anyone to do it for me. My understanding is that it's taking weeks for non-essentials to come from Amazon now. They're like a button battery but half the size so not sure they'd be easy to find elsewhere, though I imagine it's probably the same story with delivery times anyhow.
posted by unannihilated at 8:56 AM on April 13, 2020

If you order the batteries on eBay from US seller they will probably show up in 2-3 days. I have bought similar batteries on eBay in the past and never had trouble.
posted by Slinga at 9:05 AM on April 13, 2020

It’s not weeks for all non essentials from Amazon. Things take a bit longer but not all things take weeks. I’ve been getting things delivered in 2-3 days.
posted by JenMarie at 9:08 AM on April 13, 2020 [5 favorites]

If you're not certain of the temperature reading then if yours is rated that high, put it in a cup of boiling water. 212 is the temperature of boiling water.
posted by mightshould at 9:10 AM on April 13, 2020 [3 favorites]

I had to order thermometer batteries the other week, and by carefully looking at when each option said it would ship, it was possible to get them fast on Amazon. (I had to look at each listing, since some were saying shipping was a month out and others were a couple of days away.)
posted by Dip Flash at 9:10 AM on April 13, 2020 [1 favorite]

If you’re female and if reproductive age, your basal body temperature will vary based on ovulation.
posted by warriorqueen at 9:14 AM on April 13, 2020 [5 favorites]

I did a bit of my own research into this a couple weeks ago due to my own hypochondria and everything I read, like this example, says a slightly elevated temperature only counts as a low grade fever if it lasts for 24 hours or more. To me, that suggests that it’s normal for there to be slight fluctuations.

I agree with you that it’s doubtful your two thermometer are both messing up at the same time. If I were you, I would check my temperature again 1 or 2 more times today and then again next morning. I think you’re in an uncertain zone and need to gather more data.
posted by overglow at 9:28 AM on April 13, 2020 [1 favorite]

Drinking and eating can cause variation, in both directions with hot and cold stuff. The effect doesn't last super long, but can cause some variation.
posted by AlexiaSky at 9:37 AM on April 13, 2020

For what it's worth, I have a digital thermometer that must be about ten years old, give or take a year. I ended up buying a new one just as things started getting crazy because I was worried about the battery dying at the worst possible moment. I've taken my temperature now with both, one right after the other, a few times because I was wondering about the old one's accuracy, and they've always been less then a full degree apart. Actually I checked again as I typed this and both read 98.6.

Anecdote, I know, but I hope it's reassuring.
posted by DingoMutt at 9:40 AM on April 13, 2020

You should be able to get replacement batteries on Amazon within a couple days. I had to order batteries in weird sizes for our security system motion detector and door open/closed detector, and found ones that would arrive in 2 days - they showed up the next day.
posted by DoubleLune at 9:50 AM on April 13, 2020

Response by poster: I like the boiling water trick! Sadly the digital thermometers don't go up that high.

Sounds like I can and should go look for some batteries online instead of Googling symptoms and staring at my tonsils in the mirror, and that I'll just need to live with some (additional) uncertainty in the meantime, but I'm probably okay as of right now. Thanks all!
posted by unannihilated at 9:52 AM on April 13, 2020

CVS, Walgreens or Duane Reade should have the batteries. Just make note of the number etched on the back of the ones in the thermometer. A temperature isn't considered a fever unless it's over 100.4F in hospital land (I'm an RN). You also can't rely on results unless it's been at least 20-30min since you've had anything to eat or drink (including brushing your teeth).
posted by dancinglamb at 10:17 AM on April 13, 2020 [3 favorites]

Do you have a meat thermometer in the kitchen? I wanted to check the calibration of my old oral thermometer so I got some hot-ish water from the tap running at about 102 degrees on the meat thermo (thermopen) then checked my oral thermometer. It was spot on, for an anecdotal response.
posted by hwyengr at 10:53 AM on April 13, 2020 [1 favorite]

My experience with these kinds of items is that the display and the speaker fail in a noticeable way when the battery dies (display gets dim, beeps sound weird). Your specific model may vary of course.
posted by mskyle at 10:59 AM on April 13, 2020 [1 favorite]

I had an old Walgreen's digital ear thermometer, the battery of which had died. I put a new one in. It then worked, but my temp was always really low, like 92 F. I wound up throwing it away. We also have mercury thermometers. They are reliable, accurate, and do not need batteries or any maintenance other than washing. My recommendation would be to get an old-style manual thermometer.
posted by Kirth Gerson at 11:52 AM on April 13, 2020

They're like a button battery but half the size so not sure they'd be easy to find elsewhere,

There's a size code on them like CR[4 digits] or LR[2 digits] or maybe just [3 digits]. Drop that with the words "Buy Now" added into your search engine of choice and you'll be knee-deep in a list of sellers.
posted by Stoneshop at 2:49 PM on April 13, 2020

Is there any particular reason you think that old batteries would make the thermometers still work, but not be as accurate? Because I've never heard of that before.

The reason I ask is that I've had some problems with health anxiety myself, and this all sounds awfully familiar to me. It sounds a little bit like you weren't feeling great, so you you took your temperature as a way of getting an objective signal that wouldn't be manufactured by your brain (good call!). And you got that signal - you don't have a fever! So you looked for reassurance, and you got it. But now your brain is poking holes in that reassurance, and inventing a reason to think that it doesn't really count.

I've been down this road. You used two thermometers. You don't have a fever! There's no reason not to believe the thermometers.
posted by Ragged Richard at 4:46 PM on April 13, 2020 [4 favorites]

If the display is clear and bright, then they're working. Thermometers like this can be ±2 °C or so, and the sensors they use (seemingly a thermistor for a contact unit, or PIR for non-contact) won't return a reading if the controller inside the unit isn't getting enough juice. They're not like old analogue meters that might drift as the battery voltage falls.
posted by scruss at 5:01 AM on April 14, 2020

I take mine as soon as I wake up before I have eaten or drank anything, taken any medication, or engaged in any activity. So I have a very good idea of what my normal temperature range is on that thermometer for those circumstances (97.0-97.5) and now I'll know if anything changes.
posted by Jacqueline at 12:25 AM on April 15, 2020