How long will my batteries last?

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arow55
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How long will my batteries last?

Have a device (not flashlight) that uses 80uA. Uses 3 AA batteries. How long will it run? Thanks.

ggf31416
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AA alkaline cells have over 3000mAh capacity at very low current. If the cells are in series and the consumption is 80uA at the cells we have 3000 mA h / 0.08 mA = 37500 hours = about 4 years if the device can use all the cell capacity.

arow55
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Thanks for doing the math. People on this forum are really helpful. Not like some folks on firearm forums.

xxo
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If they are alkalines, they may start to leak before they are fully drained. Enegizer L91 lithiums should last about 5 years and won’t leak.

arow55
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xxo wrote:
If they are alkalines, they may start to leak before they are fully drained. Enegizer L91 lithiums should last about 5 years and won’t leak.

It’s a carbon monoxide detector and has low battery alert. But lithium sounds smart.
tatasal
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xxo wrote:
If they are alkalines, they may start to leak before they are fully drained. Enegizer L91 lithiums should last about 5 years and won’t leak.

Not in my case: http://budgetlightforum.com/node/63880

They did leaked!

Th558
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I only trust eneloops

arow55
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Th558 wrote:
I only trust eneloops

Have maybe 50 of them but would probably set off low battery warning.
ggf31416
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Eneloops come at 1.33V from the factory. If eneloops set off the low voltage warning then it will only use less than 50% of an alkaline cell. In that case you are better off with the L91s, which will keep a stable voltage until almost fully depleted.

If there is any device in your house that could generate CO you probably shouldn’t use alkalines as the detector failure would expose you to significative health risk.

arow55
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ggf31416 wrote:
Eneloops come at 1.33V from the factory. If eneloops set off the low voltage warning then it will only use less than 50% of an alkaline cell. In that case you are better off with the L91s, which will keep a stable voltage until almost fully depleted.

If there is any device in your house that could generate CO you probably shouldn’t use alkalines as the detector failure would expose you to significative health risk.


Will give eneloops a try. Can’t hurt since I got 3 identical detectors.
kennybobby
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What is the model of the CO detector and how do you know that it only draws 80uA? Most battery operated detectors recommend to change batteries every 6 months.

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arow55
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kennybobby wrote:
What is the model of the CO detector and how do you know that it only draws 80uA? Most battery operated detectors recommend to change batteries every 6 months.

Less than 80uA was in the instructions specs. Never used CO detector before. Reports on Amazon said many years of use.
arow55
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Put eneloops in one and not chirping yet.

flydiver
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I use 9v rechargeable lithium in my smoke detectors. I put a piece of easily removable tape on the side and note the date. I also make a calendar alert to check and re-charge every 6 months or so. If it’s a pain to get at I put primary lithium in it.

arow55
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Got eneloops in two and alkaline in one. Will see how long they last.

wle
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hard to know

a. they may leak before failing

b. the device will define its own failure(possibly) ie it may be monitoring voltage and decide that it is too low, before the mAH are used up

wle

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Hobbyfotograaf
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The minimum voltage for the CO detector to work without giving a low battery warning is important if you want to know if it will work with nimh-cells.
The working voltage of nimh is only 1,2V per cel, the maximum voltage is a bit higher, but the voltage drops very fast to 1,2V.
Alkaline cells have a higher voltage (when they are new) and with a very low load it will take a lot longer to drop to 1,2V than nimh cells.
Lithium AA cells start even higher (about 1,7V) and with a very low load it will take even longer before they get to 1,2V.
But lithium AA cells are more expensive than alkaline.

I had problems with an outdoor temperature/humidity sensor of a weather station, with alkaline cells that sensor only worked for a few months, it stopped working when the alkaline AA cell was 1,45V.
Now there is a lithium AA in that sensor for more than one year, and it is still working.
https://nl.aliexpress.com/item/32796221501.html?spm=a2g0o.productlist.0....
I have smoke detectors with 9V batteries that will give low battery alert when the battery voltage is only dropped to 8,5V.
Only about 20% of the battery capacity is used when the voltage of a 9V battery is 8,5V…
I ordered these for the smoke detectors (but they are not delivered yet): https://nl.aliexpress.com/item/32779884127.html?spm=a2g0s.9042311.0.0.99...

These smoke detectors will never work with rechargeable 9V nimh batteries, and that could also be the same for the CO detector because the voltage of nimh is too low.

arow55
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Hobbyfotograaf wrote:
The minimum voltage for the CO detector to work without giving a low battery warning is important if you want to know if it will work with nimh-cells.
The working voltage of nimh is only 1,2V per cel, the maximum voltage is a bit higher, but the voltage drops very fast to 1,2V.
Alkaline cells have a higher voltage (when they are new) and with a very low load it will take a lot longer to drop to 1,2V than nimh cells.
Lithium AA cells start even higher (about 1,7V) and with a very low load it will take even longer before they get to 1,2V.
But lithium AA cells are more expensive than alkaline.

I had problems with an outdoor temperature/humidity sensor of a weather station, with alkaline cells that sensor only worked for a few months, it stopped working when the alkaline AA cell was 1,45V.
Now there is a lithium AA in that sensor for more than one year, and it is still working.
https://nl.aliexpress.com/item/32796221501.html?spm=a2g0o.productlist.0....
I have smoke detectors with 9V batteries that will give low battery alert when the battery voltage is only dropped to 8,5V.
Only about 20% of the battery capacity is used when the voltage of a 9V battery is 8,5V…
I ordered these for the smoke detectors (but they are not delivered yet): https://nl.aliexpress.com/item/32779884127.html?spm=a2g0s.9042311.0.0.99...

These smoke detectors will never work with rechargeable 9V nimh batteries, and that could also be the same for the CO detector because the voltage of nimh is too low.

have envelops in two for a couple days and so far so good. If I can get 6 months before charging would be happy.
wle
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interestingly, carbon zinc, the very cheapest batteries, have the highest initial voltage, i have measured some over 1.61V

wle

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Lightbringer
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Wellp, CO detectors (at least the sensors) do “wear out” over time. That’s why a lot of ‘em have sealed Li cells inside, and you just toss ‘em when the cell’s spent.

 

Eg, from https://protechsecurity.com/how-long-do-smoke-and-carbon-monoxide-detect...

Carbon monoxide detectors last between five and seven years. The recommendation is to replace them every five years because their ability to detect carbon monoxide is questionable after that point.

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