Basic Battery Question

Hi all. I have a couple of questions regarding the batteries for our lights. Please let me know if my statements are correct, and if not, why not.

1. Given the exact same flashlight, a 3.7v 18650 lithium ion battery with a higher mAh than the same battery with a lower mAh will have the same brightness but shorter run times.

2. Given the exact same flashlight, a 3.7v RCR123 lithium ion battery will be brighter than a 3.0v lithium primary battery. Which generally has longer run times?

3. Given the exact same flashlight, (2) 3.7v RCR 123 750 mAh lithium ion batteries will be brighter than (1) 18650 2200mAh lithium ion battery, but the 18650 will have longer run times.

4. Given the exact same flashlight, (2) 3.0v lithium primary batteries will be brighter than (1) 18650 2200mAh lithium ion battery, but the 18650 will have longer run times.

5. A 3.7v 14400 lithium ion battery will have the same brightness as a 3.7v RCR123 lithium ion battery and a3.7v 18650 lithium ion battery.

Thanks in advance!
Frank A.

For #1 you are correct.

Generally, for the other questions, it depends entirely on the particular driver used in the light.

The LEDs brightness depends on amperage, not voltage. In some cases, when the driver is not regulated above a certain Voltage, the light will revert to being direct drive. This is when the LED is being driven at whatever amperage the LED will draw from a battery of a particular size, until the battery voltage drops to a set level, at which time the driver can again regulate current.

A good primer can be found here.

So, I will recommend a bit of reading before you a few nice lights.

1. This is general true but does depend on the internal resistance of the battery. A high resistance battery(usually cheap quality) can not give as much current as a low internal resistance battery(quality) at high currents. I=V/R ohms law.

2. If its a single cell light this is general true. The driver has to buck down the voltage of a 3.7v RCR123 and usually will give a more constant current. The driver would either boost the voltage for the 3.0v battery or become direct drive. Either way its going to give less current. Using less power with less light for a longer time.

3.Depends on the driver but is general true. With 2 batteries 7.4v the driver would buck the voltage all the way threw the run time. Giving a constant brightness. With a single 3.7v battery the driver would buck the voltage down also but at some point the voltage will be less than the forward voltage of the led and other resistance losses in the light (switch, contacts, wire and flashlight body). When this happens most drivers become direct drive and the battery gives what ever voltage it can give until depleted. As the voltage decrease beyond the direct drive point the current goes down helping in giving a longer run time but at less light output. Some drivers are buck and boost which would help giving a constant output. The 18650 has more stored energy than the 2 RCR123 so will last longer but not necessarily at lower light outputs. Depends on driver.

4. Same as number 3.

5. General yes. Would depend on the current the battery was being subjected too and the internal resistance of the battery. At low currents 1 to 2 amps probably not much difference at all between them. At higher currents the 18650 would probably win. But does depend on the quality of the batteries used.

I'll bite!

1. Yes, higher capacity = better runtime
2. RCR123 will be brighter but in some cases where the light is well-regulated, you can get the same output from a RCR123 and a CR123. Which has better runtimes? the RCR123's. But there are new CR123's with 1500mAh (4Sevens) these may have good runtimes.
3. Yes, but for good regulated lights, output is almost identical, but definitely runtimes go to the 18650.
4. Same as 3.
5. yes, but the runtime of the 14500 is better than the RCR123 but second only to the 18650.

Frank A. said:

Hi all. I have a couple of questions regarding the batteries for our lights. Please let me know if my statements are correct, and if not, why not.

1. Given the exact same flashlight, a 3.7v 18650 lithium ion battery with a higher mAh than the same battery with a lower mAh will have the same brightness but shorter run times.

2. Given the exact same flashlight, a 3.7v RCR123 lithium ion battery will be brighter than a 3.0v lithium primary battery. Which generally has longer run times?

3. Given the exact same flashlight, (2) 3.7v RCR 123 750 mAh lithium ion batteries will be brighter than (1) 18650 2200mAh lithium ion battery, but the 18650 will have longer run times.

4. Given the exact same flashlight, (2) 3.0v lithium primary batteries will be brighter than (1) 18650 2200mAh lithium ion battery, but the 18650 will have longer run times.

5. A 3.7v 14400 lithium ion battery will have the same brightness as a 3.7v RCR123 lithium ion battery and a3.7v 18650 lithium ion battery.

Thanks in advance!
Frank A.

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