Battery Capacity Test (Cold Weather and High Current Use)

The Capacity of AA Batteries

The capacity of AA batteries is usually stated in milliamp hours (mAh). The most common test for capacity is to apply a constant load to the battery until its voltage reaches a certain value. One standard test for AA batteries is to apply a 250 mA load until the battery voltage drops to 0.8 V (most devices cease to function below this level). For example, let's say it took 12 hours to discharge a battery to 0.8 volts, then the capacity would be 250 x 12 = 3000 mAh. In theory, this 3000 mAh battery would be able to produce 30 ma for 100 hours (3000/30 = 100) or 5 ma for 600 hours (3000/5 = 600), etc. However, capacity is sometimes affected by temperature and the current load. For comparison, we have completed this standard capacity test on Energizer AA Alkaline, Energizer AA Ultimate Lithium, XTAR Lithium Ion Rechargeable and XTAR NiMH AA rechargeable at room temperature and in a freezer at 5° Fahrenheit with a 245 ma load.

Battery Tested	Room Temperature (72° F)	5° F	% of Room Temperature
Energizer AA Alkaline	2181 mAh	728 mAh	33%
XTAR NiMH AA Rechargeable	2663 mAh	2197 mAh	83 %
XTAR AA 3300 Lithium Ion Rechargeable	2016mAh	1669 mAh	83%
Energizer AA Ultimate Lithium	3430 mAh	3332 mAh	97%

 

Alkaline batteries are significantly affected by the 5° temperature. Only 33% of its room temperature capacity is available at 5°. If this battery is returned to room temperature, its remaining capacity of 1453 mAh (2181 - 728 = 1453) will be available. We have had cameras with alkaline batteries stop taking pictures during the coldest part of the winter and then return to working again in early spring. The available capacity of lithium batteries was not significantly affected by the 5° temperature, and NiMH cells were only moderately affected.

Alkaline battery capacity tests also vary with the current load used. If a test is completed with a load of 100 ma instead of 250 ma, a higher milliamp capacity results. Likewise, if a load of 500 ma is used, a smaller milliamp capacity will result. The other two types of battery chemistries are not significantly affected by current load.

Battery Tested	100 ma Load	250 ma Load	500 ma Load
Energizer AA Alkaline	2608 mAh	2181 mAh	1575 mAh
XTAR NiMH AA Rechargeable	2754 mAh	2663 mAh	2440mAh
XTAR AA Lithium Ion Battery	1923 mAh	2016mAh	2036 mAh
Energizer AA Ultimate Lithium	3475 mAh	3430 mAh	3235 mAh

 

Unfortunately, the only reliable way to measure a lithium battery's remaining capacity is to run the tests above. Are there other ways of testing a battery without discharging it to a non-usable state? You could check a battery's voltage with a multimeter. However, that's not a good test of a battery's remaining capacity or condition, as it does not place a significant load on the battery when measuring voltage. A battery might have a voltage reading of 1.5 v., but when a load is placed on it, the voltage may drop to below 0.8 volts in a few seconds. Without the load, you would think the battery was good.

There are commercially available battery testers that perform a capacity test by applying a load to the battery and then reading the voltage. This voltage is compared to predetermined values from a discharge graph to render a fairly accurate estimate of remaining capacity. These testers perform adequately on alkaline batteries, as the discharge graph is consistently predictable. But Lithium and NiMH batteries produce a discharge curve with a constant voltage throughout the discharge cycle, making capacity predictions unreliable. Most trail cameras display a battery meter on the LCD screen and function much like these commercial testers.

Which of the three types of batteries should you select to use in a trail camera for the best performance? Hands down, from the tests we have completed, that would be the Lithium, or lithium-ion battery. Could you use Alkaline of NiMH? Yes, but it would depend on several factors that would be unique to each trail camera. The following is a list of things to consider:

1. Temperature where the camera is placed?
2. Will the camera function with the lower 1.2 volts per cell of a NiMH battery?
3. Are you willing to keep NiMH batteries charged on a 2-3 month schedule?
4. Will the camera be shooting lots of night videos?
5. Is this a cellular camera that requires more power per photo transmission?
6. Are you concerned about Alkaline battery leaks and corrosion?
7. Will the camera be left unattended for months?
8. What are the power requirements for the settings I have selected (burst mode, video mode, time lapse, etc.)?

 Thanks for reading!

- Charles Padgett, TCP Technician