CR2032, but with more Ah?

[eggsalad]

I have a device (reflex sight) that uses a single CR2032. But it kinda eats batteries like a fat kid eats free candy. (Not the fault of the device, I use it differently than intended.)

I can add an external battery, and my first thought was an 18650, because I own tons. But the 18650 has a significantly higher voltage, nominally 4v vs the 3v of a 2032. So that's out.

A 123a seems to have a similar voltage range of the 2032, and somewhere in the neighborhood of 5 times the Ah.

My gut feeling is that a 123a in a suitable holder would operate the device just fine. Am I thinking correctly?

 

[LEDphile]

All of the CRxxx batteries use the same chemistry, and so should be interchangeable electrically (assuming you are moving up to a larger size). So a CR123 would be an appropriate replacement for a CR2032, at least electrically

 

[idleprocess]

My gut feeling is that a 123a in a suitable holder would operate the device just fine. Am I thinking correctly?

Probably, assuming the device has proper current limiting rather than depending on coin cells' significant internal resistance.

 

[DaveTheDude]

I'm just curious as to what "off-label" use you put the reflex sight to. (No grammarian purist replies, please; I'm aware of the dissonance, but this is an informal conversational forum. Thank you.)

 

[Dave_H]

Probably, assuming the device has proper current limiting rather than depending on coin cells' significant internal resistance.

Quite correct, and important to check; and it's not just coin cells, a number of 3xAAA flashlights
do this.

Dave

 

[JimIslander]

I suggest it is the sight's fault.

Buy an Aimpoint T2. Leave it on all the time and it will run 50,000 hours on a CR2032, almost 6 years.

 

[LEDphile]

A few numbers around internal resistance: a fresh CR2032 has a rated internal resistance of around 10 ohms, compared with the roughly half an ohm for the CR123. That's about a .1V drop on the CR2032 for a 10mA LED load, and negligible drop on the CR123. Probably not an issue for blue or green LEDs, but for red or amber, could make a difference.

The safe answer would be to add a 10 ohm resistor to your external holder to make the problem moot.

 

[eggsalad]

Responses to all, I'm too lazy to respond to everyone individually...

To Dave the Dude: In Live Entertainment, reflex sights are used to aim follow spot lights. It's most common to use a Telrad telescope finder, but those are big and bulky, so I prefer a reflex finder intended for f1rearms. It's also cheaper, if you buy a cheap import.

To JimIslander: the Aimpoint T2 is a very nice sight, but the $884 difference between that and my $18 import sight will pay for a whole lot of batteries.

In sum, I appreciate the input, but in the big picture, it all seems a bit more trouble than it's worth. I'll just buy CR2032 in bulk.

 

[LEDphile]

Ah, for that application, I'd be tempted to try a pair of AA batteries in series instead of the lithium. L91s wouldn't be a good choice (voltage too high), but alkalines should be fine and even NiMH might work. Fresh voltage on the alkalines will be a touch high, but if you've got a bucket of half-used batteries (perhaps from wireless packs), those would be just about perfect.

 

[JimIslander]

To JimIslander: the Aimpoint T2 is a very nice sight, but the $884 difference between that and my $18 import sight will pay for a whole lot of batteries.

Yep, that's 5893 battery's worth, so you could change batts every day for the next 16 years and it will still cost less.