Smoke Detector Batteries: Replace or Test
Introduction
It is that time of the year that we all get advice to replace the batteries in the home smoke detectors. The prevailing advice is to change the batteries in the fall and again in the spring.
The recommendation we received was to do this chore on the Summer and Winter Equinox in June and December. This year, I heard a news channel recommending the smoke detectors be service at the Daylights Savings time change, in the Fall and in the Spring. Both recommendations seem a bit ambiguous.
The problem
This may fall into the category of Pet peeve. In my home, I have been blindly following that advice until this year. I went ahead to the hardware store to buy the 9Vdc batteries for my 6 smoke detectors. I replace them twice a year without question. Until this year.
Inflation has affected the cost of batteries like everything else. Buying six batteries required me to buy 2 packages of 4 batteries each at the cost of $20 for each package of 4.
This became an incentive for me to research just why I was replacing the batteries twice a year. It turns out that the manufacture of smoke detectors recommends testing them once a month. This is conducted by pressing the test button and waiting for the detector alarm to beep. A solid loud beep says a good battery. A weak beep says time to replace the battery. This would keep battery replacement down to once a year or perhaps longer.
Being an Electronic Engineer, I know that this is not the best way to decide if the battery needs to be replaced. The industry standard is to evaluate the battery with a Volt-Ohm-Meter (VOM) Multimeter. These are readily available at any home improvement store or hardware store. I have both Analog and Digital types in my tool inventory.
Here is how to decide the useful life of the 9Vdc battery.
Watch the video.
The presenter goes through a test with a load that is interesting, but unnecessary. The simple meter test for voltage is sufficient to decide to replace. The video shows that a voltage below 6 Vdc is considered a dead battery. We don’t want to wait until the battery is completely dead. The smoke detector low battery chirp will typically start at 7.2 to 7.7 volts, depending on the model of the alarm. Any meter reading around 8Vdc would say the battery needs replacing.
The Test
I have done this test with my $7-dollar analog meter and with a $200 Digital Multimeter. First I test new batteries out of the package and then test the batteries removed after 6-months of service.
New Batteries
I used both types of meters to evaluate the batteries.
Analog meter tests all the batteries low, around 8.5 Vdc.
I was suspicious of the result, so I did a more thorough job of setting up an analog meter. I adjusted the indicator needle to read exactly on the zero mark for the 10Vdc range. Additionally, I made certain I was reading directly above the meter so I could see and align the needle in the mirror on the face of the scale. This helps eliminate inaccuracies due to parallax.
The new readings were 8.9-9.0 Vdc.
Digital meter test showed all batteries more than 9.6Vdc
Batteries removed after 6-month service.
Analog meter test with the new setup showed 8.8 – 9.0Vdc
Digital Meter reading 9.4 – 9.6
Analog meters are getting more difficult for me to read as my eyes get older. I prefer the digital meter. However, even with analog meter inaccuracies, I would not have replaced any batteries based on the reading from either meter. The drain on the batteries is too small to need replacing in just 6 months.
The equipment and method
Low-cost analog VOM Multi meter
Analog VOM Multimeter
Great tool in its day. However, setting and interpreting the needle potion can be difficult
This is cheaper, but more intricate to use. Once setup, the user needs to interpret the positioning of the needle on the correct scale. With 7 reading scales, this can be challenging for the new user.
· Set the dial to the 10 DCV scale.
· Plug in red lead into the Red + connection!
· Plug the black lead into the Black – connection.
· Orient the test battery so the red lead touches the Plus terminal of the battery, and the Black lead touches the Negative terminal.
· Read the voltage on the second (Red) scale from the bottom number 1-10.
· If you were to set the meter to the 50DCV scale, you would still get a reading, but you would be reading the voltage on the Black scale number 1-50.
· Any reading below 8Vdc would show a weak battery.
I also used my Fluke 26III Meter I have used daily for over 40 years. This meter today will cost about $250. There are any number of lower cost digital meters available in the under $30 range. The setup on this meter does not require fussing with needle alignment to get an accurate reading.
Fluke 26 III from 1990’s
Digital VOM Multimeter
Modern Digital MultiMeters include a HOLD Button. Fumbling with your hand full of meter lead and reading the meter at the same time can lead to some unsafe conditions.
Think about trying to test the voltage in your home’s main power panel. You need both hand to manage the meter leads. How can you focus on the meter leads and read the meter at the same time? HOLD make this a safer operation.
This meter uses icons or pictographs to show the function on the switch. It has 2 Voltage scales, one for AC voltage shown with Large V under a wavy line. The DC voltage is shown by a large V under a straight line and a dashed line.
· There are 4 connectors at the bottom of the meter. DC voltage uses the 2 connectors on the right side.
· Red lead into the red connector.
· Black lead into the Black COM connector.
· Touch
· Red lead to Positive side of battery.
· Black lead to the Negative side of the battery.
· You read the voltage in the display directly without needing interpretation.
Conclusion
There are 3 ways to manage the batteries in your smoke detectors.
· Method 1 (Great if you don’t worry about cost)
o Replace batteries twice a year.
o You will always have a fresh battery in your smoke detector.
· Method 2 (Should be done with Method 1&3)
o Press the Test Button once a month!
o Replace the battery when the beeper sounds weak.
· Method 3 (More work but more ecologically and financially sound)
o Use a Multimeter to evaluate the actual battery voltage!
o Replace any battery reading below 8Vdc!
Any time you don’t throw something in the trash to send to the landfill, you are providing a better service to the whole community.
