Return of the (9V) Battery Boy

What can you do with a 9 volt battery? Not much, it seems.

Whenever we switch between daylight savings and standard time, we get reminders to change the batteries in our smoke and carbon monoxide detectors. My carbon monoxide detectors take AA batteries, but the smoke detectors take the square edged 9V batteries.

It’s a pain disposing of batteries because they are household hazardous waste and need to be taken to a household hazardous waste depot. So I have a big container of batteries just waiting for me to take them to a depot. (I will get around to it–someday.) Of course, there are old AA and AAA batteries in my container too. What particularly bothers me about the 9V batteries, though, is that I know many of them still have some life in them. The whole point of taking them out of the smoke detectors every six months is to do so while they’re still doing the job. So what else are they good for? I will have some suggestions, but first, more about the smoke detectors.

I have two different models in my house just now. One is a Kidde Model i9070CA, about a year old. The other smoke detector is an SA320 from Dicon Global Inc. (I believe the manufacturer was First Alert.) It’s also about a year old. Each uses ionization technology, and is supposed to be good for 10 years.

The Kidde user manual says: "WARNING! Removal of the smoke alarm battery will render the smoke alarm inoperative." (Don’t you love these things?) It also says:

Use only the following 9 volt batteries for replacement:
Carbon-Zinc Type Eveready 216 or 1222
Gold Peak 1604P or 1604S
Alkaline Type Energizer 522
Duracell MN1604 or MX1604
Gold Peak 1604A
Panasonic 6AM6, 6AM-6, 6AM-6PI,
6AM6X or 6LR61(GA)
Lithium Type Ultralife U9VL-J

WARNING! Use only the batteries specified above. Use of different
battries than the recommended ones, may have a detrimental effect
on the smoke alarm. …

The Dicon user manual says:

The Eveready 216, 522, 122, 1222, Duracell MN 1604, MX 1604 and
Gold Peak 1604P/S/A are the only acceptable batteries for use
in this smoke alarm. …
WARNING! Use of non-recommended batteries may be
detrimental tothe proper functioning of the alarm.

If you believe the advertising, you could use the GP Lithium 9-volt in a smoke detector. I don’t know. Since I’m likely to be buying new smoke detectors before the old ones are useless (see below), I’ll probably do a little bit of experimenting. In any event, readers of this column should note that the author is an uninsured, unlicenced amateur whose opinions should never be relied upon. (You all were thinking there wasn’t going to be anything legal about this column, weren’t you?)

None of the listed batteries is a rechargeable battery. Why not? It probably won’t surprise you to learn that I’m not the first person to ask this question. Here are a couple of things that I’ve found worth reading: "The 9-Volt Battery Conspiracy" (; and "Smoke alarms that run on AA or AAA batteries?" (

The "conspiracy" article, originally written in 2007, had attracted 175 comments as of November 14, 2011, most of them useless or spam. So here are my personal highlights. In comment 4 (May 7, 2007), "Gel" said:

Standard alklaine or zinc batteries will gradually deteriorate over 2 or 3 years; when voltage gets to low trigger warning level (around 7.5v) alarm then has to beep for 30 days once a minute(to tell you to change it); this so complies with product standard. Rechargeables when they go off, drop voltage like off edge of a cliff, so won’t give the all important 30 days protection.

In comments 51 and 52 (February 6, 2010), "don’t want to tell" said:

if you split open a good quality 9v battery you will find 6 aaaa batteries. once you have the 6 aaaa batteries out of the 9v you can put them in any thing that uses aa or aaa. thus giving you a use for these half dead batteries. you just need to use a piece of the metal from the 9v connector lead as a spacer. to make the spacer you just get a small piece (1/2 inch or so) of the metal from inside of battery (it runs the length of the battey and is about 1/4 inch wide) and make a v out of it. once you have your spacer and the batteries just put the battery in the place of the aa or aaa and use the v as a power connecting wedge.

In comment 61 (May 14, 2010), "Saving money" said:

We have a few Kidde brand smoke/carbon monoxide detectors and they use 3 AA batteries each. they are out there!

In comment 95 (December 14, 2010), "J. Laurence" said:

Until about the mid-1990s, Radio Shack sold one of their brands of “Pocket Radio” that ran on 9-volt batteries. … I discovered that these AM/FM radios were good for just three or four days on those notorious 9-volts, while other AM/FM pocket radios on just two AA’s lasted three times longer … In conclusion, the 9-volt class of batteries may only make good sense for basically dormant devices … versus, say, a (pocket) radio, which is generally supposed to continuously run for several hours at a time.

In comment 121 (June 2, 2011), "me" said:

AA and AAA batteries have the same voltage just different current capabilities. So using 20 AAA batteries would give you 30V and prob fry your detector.

The "AA or AAA batteries?" question, originally posted November 3, 2009, has attracted seven responses, but with a much higher signal to noise ratio than the "conspiracy" posting. On November 3, 2009, "JohnR66" said:

A rechargeable has more of a steep voltage drop near the end of discharge as compared to an alkaline battery. It could be possible to miss the low voltage signals and go unprotected. … Not sure why the high voltage of a 9 volt battery is needed. perhaps it helps with the current flow in the ionization chamber.

In November 4, 1999, "Illum" said:

Smoke alarm batteries need that high voltage to sound the alarm when the photoreciever does close the circuit, but 99.99% of the time they die from the quiescent current drawn from the circuit. I’m pretty sure its in the <100 µA range because the PP3 [or the ANSI standard 1604A] batteries in alkaline form has only approx 550mah of juice, Carbon-zinc as about 350mah, but thats a conservative estimate.

It sounds perfect for carbon zinc cells because thats what they’re designed for: low current draw, long load time. Alkalines are half and half because they tend to [in my observation with 5 kidde alarms in the house, 3 of them beside my lithium pile] self discharge faster than the carbon zincs [and therefore chirp sooner] within the same amount of time before I change it [~1yr].

No point at all going for rechargeables because NiMH 9Vs are like ~150mah [if even close]

Also on November 4, 2009, "LEDMaster2003_V2" said:

Alarms the run on AAs?
Kidde CO/Smoke combo (x3)
Kidde Wireless Smoke Alarms (x3)
First Alert OneLink alarms (x2)
First Alert SCO7 (x2)

I wish I had done this research before buying my one-year-old detectors. Oh well. The Kidde Silhouette 900-0252, for example, runs on normal household 120V AC power, and comes with a sealed rechargeable backup battery that doesn’t need to be replaced. Alternatively, there’s the Kidde Talking Combo Smoke/CO model 900-0102, which takes three AA batteries. The manual says:

Replace batteries with one of the following
approved brands:
Duracell MN1500 or MX1500
Energizer E91

WARNING! Use only the batteries specified. Use of
different batteries may have a detrimental effect on the
Smoke/CO alarm. …

For some reason, I wasn’t able to find the First Alert SCO5CN Combination Smoke and Carbon Monoxide Alarm on the Dicon Global site. In any event, it also runs on two AA batteries. The manual says:

Your Smoke/CO Alarm requires two standard AA batteries.
The following batteries are acceptable as replacements:
Eveready Energizer E91.

What about using AA rechargeable batteries in these? The concerns listed above are echoed in the Wikipedia article on smoke detectors:

Common NiMH and NiCd rechargeable batteries have a high self-discharge rate, making them unsuitable for use in smoke detectors. This is true even though they may provide much more power than alkaline batteries if used soon after charging, such as in a portable stereo. Also, a problem with rechargeable batteries is a rapid voltage drop at the end of their useful charge. This is of concern in devices such as smoke detectors, since the battery may transition from "charged" to "dead" so quickly that the low-battery warning period from the detector is either so brief as to go unnoticed, or may not occur at all.

What about an "uncommon" rechargeable battery with a low self-discharge rate? A NiMH battery like the Maha Powerex Imedion 9.6V, or the Sanyo Eneloop AA? (See also "Technology" (, "Educate Me! About Batteries" ( and "Review of Imedion" (YouTube).) T.D. Wood’s "How to Choose Batteries" (, and the anonymous "Rechargeable Batteries and Chargers: A Personal Perspective" ( provide good introductions to the subject. The latter still advises caution where smoke detectors are concerned. (Compare, for example, the capacity of the Maha Powerex Imedion 9.6V with the Milliamp Hours performance of the Eveready 1222.)

Greenbatteries’ "AA and AAA Battery FAQs" ( interestingly tells us that AA size rechargeable lithium ion batteries are typically 3.6 or 3.7 volts, not the normal 1.2 or 1.5 volts. In other words, they would probably just fry your smoke detector.

So what else can you do with your half-discharged smoke detector batteries? Lots, with the AA kind, of course. It’s more of a challenge to find other uses for the 9V batteries. I made the rounds of the stores. A clerk at Canadian Tire managed to direct me to the Electrohome AM/FM Projection Clock Radio at least. (It uses a 9V battery as a backup. Still not a great way to drain the battery.) The folks at Canada Computers will sell you a Powerex 9V battery, but they couldn’t tell me where I could actually use one. No luck at The Source, Radio World or Henry’s either.

I did have a bit of luck at Pickering Markets. One of the vendors there (I forget which one) suggested a DT830B digital multimeter. One of these is useful for many things. In fact, not only is it powered by a 9V battery, but you can even use it to check the voltage on another 9V battery.

I was cheating, of course, when I went to the Crossroads Trading Post & Flea Market in Brantford. I found a 35-year-old but fully operational, 9V powered TI-1450 calculator. They also had several 9V powered transistor radios, including a Little Green Sprout model made in Hong Kong.

Since I like to go to hiking-type shops sometimes to look for gadgets, I also tried Tent City in Concord, and Adventure Attic in Dundas. No luck. I did get a lead at Oakville Outdoors & Surplus Exchange. The owner didn’t have any in stock, but he tipped me off to the Pak-Lite. So I got one by mail from Oregon. It’s a little cap that snaps on to the top of a 9V battery, and powers two bright LEDs. It makes a great little flashlight. I don’t love it as much as my NightStar CS Magnetic Force Flashlight, but it’s still pretty sweet.

I was hoping to find something similar to the Sanyo Hand Warmer for rechargeable 9V batteries, but I didn’t. I did find a nice video from Make Magazine on YouTube showing how to make a "Personal Portable Heater" using AA batteries and some winding wire. There’s no reason you couldn’t do the same with a 9V. At least I can get that and some battery snaps at The Source.

Of course, there’s also stuff like “How to Make a Small Personal Heater” on WikiHow. Just put two 9V batteries together, they say. As the authors do note, however, you could easily hurt yourself doing that, so be careful.


  1. Careful with that big container of batteries! Shuffled around, batteries of various sizes can align to form a circuit, causing a fire hazard. 9 volt batteries especially, with both terminals at one end, are prone to accidential shorting, even if they are partially discharged.

  2. Spend less time worrying about what kind of battery to use in your smoke alarm and more checking what technology is used to detect smoke. Most likely it’s Ionization rather than Photo-Electric. The International Association of Fire Fighters (IAFF) has called the banning of ionization detectors as they are MUCH slower to trip than photo-electrics.

    Also ensure you are replacing life safety detectors at the end of their rated life. Typically 10 years for smoke detectors and 5 for carbon monoxide detectors.

    This is the stuff that will really make a difference in saving someone life!