# Need help determining LED run time given a certain battery

I have struggled to determine if a single CR2032 battery is sufficient to run some LED lights for a long enough period to replace the 2 AAA recommended for a DIY build. I'd like to use CR2032 instead to save on weight/size.

I know a CR2032 is 3v which is comparable to 2 AAA in output, but the lifespan of the battery is the question. With a CR2032 only having around 200mAh and 2 AAA having around 2000mAh, that's a huge difference.

I will be running three of these LEDs. The specs say they are 1.35v, but I don't know how to convert that into something helpful in determining the power consumption in mAh :( (https://www.amazon.com/uxcell-Infrared-Emitter-Emitting-TSAL6200/dp/B07W4LT2Z7/ref=sr_1_3?crid=1SIF2TQJJ3BRG&keywords=uxcell+5mm+infrared+transmitter&qid=1669661115&sprefix=uxcell+3mm+infared+transmitter%2Caps%2C190&sr=8-3)

If I can figure out how to determine the consumption, it'd be pretty simple to determine how many hours of use a 200mAh CR2032 would last. Hopefully, someone knows how to determine the consumption rate of these LEDs.

I saw some generalized search results that indicate a 5mm LED has, on average, a 20 mA current. Does that mean I can do 20mA * 3 LEDs for 60 mA per hour of consumption or 3.3 hours of battery life from a 200 mAh battery?

• Hint a 20mA current for 1 hour is 20mAh. Commented Nov 28, 2022 at 19:00
• Lithium coin cells are intended for low (microampere range) loads, not for driving LED's. You won't get 200mAh at that level of drain. Not even close. Maybe 1/10 or even less than that. Consider the Eveready datasheet for CR2032.. data.energizer.com/pdfs/cr2032.pdf.. The values/charts shown are for a drain rate of 0.19mA. i.e. about 300x less than what you propose. I won't go into 'why', but generally the faster you suck current from any battery, the less total power will be available from it. (varies by chemistry...) Commented Nov 29, 2022 at 2:42
• If size/weight are important, consider a small Li-Ion pouch cell (3.7V) or maybe to stay at 3V, alkaline AAAA cells (They exist) or N cells (they also exist) would be suitable. Commented Nov 29, 2022 at 2:43

## 2 Answers

Searching for "TSAL6200" returns this datasheet. Assuming you are actually getting the device advertised and not counterfeits or straight-up different parts, the maximum continuous forward current is 100mA. I don't know if you intend to run them continuous, pulsed, at full power, or something less, but let's assume you are running all three at 100mA. 3 LEDs at 100mA gives a total current draw of 300mA, so your AAAs could run them for perhaps 6 hours from the data shown in this datasheet, assuming your driver was capable of handling discharge to 0.8V/cell and is reasonably efficient (no resistors or 78xx regulators).

AAAs are rated to provide low hundreds of mA of current, as you can see from the datasheet, there's actual performance data for that amount of current. 2032s, on the other hand, are not. Looking at a 2032 datasheet, "standard continuous discharge current" is 300 uA, "maximum continuous discharge current" is 3mA, and "maximum pulse discharge current" is 50mA. The capacity of 265mAh might be close to the AAA value, but that's assuming you are pulling current at orders of magnitude less than what you are going to need to power your IR emitters. Replacing AAAs with 2032s in your circuit will result in a design that burns through coin cells in minutes. Either use AAAs or get a small Li-ion battery pack.

• Do resisters impact this at all? Commented Nov 29, 2022 at 4:46

To estimate this, you can divide the battery capacity (in mAh a.k.a. mA-hours) by the current that flows through the circuit (in mA) to get hours.

The current flow depends on the circuit - the person who designs the circuit has the power to decide what they want it to be. You can measure it with your multimeter, if you have one.

As a point of reference, 20mA will make an LED shine bright enough that makes you want to put two layers of tape over it so you can sleep. It won't come close to lighting up a room, though. If your LEDs are dimmer than this, they're using less than 20mA. (I have a theory that electronics engineers learned the magic number 20mA when they were in university, and now that LEDs are 30 years better and make way more light for the same mA, those engineers still use 20mA.)

If you have more than one LED, the mA adds up. It's possible to connect LEDs in series, so that the volts add up instead of the mA, but they wouldn't have done this in something that's designed to use a 3V battery.