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 test for capacity is to put a constant load on the battery until the voltage of the battery reaches a certain value. One standard test for AA batteries is to put a 250 ma load on the battery until the battery voltage is reduced to 0.8 volts. 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, the capacity is sometimes affected by temperature and the amount of the current load. For comparison, we have completed this standard capacity test on Energizer AA Alkaline, Energizer AA Ultimate Lithium, and Tenergy AA Premium NiMH 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%
Energizer AA Ultimate Lithium 3430 mAh 3332 mAh 97%
Tenergy AA Premium NiMH 2577 mAh 2213 mAh 86%

 

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 working again in early spring. The Lithium available capacity was not significantly affected by the 5° temperature and the NiMH was moderately affected.

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

 Battery Tested 100 ma Load 250 ma Load 500 ma Load
Energizer AA Alkaline 2608 mAh 2181 mAh 1575 mAh
Energizer AA Ultimate Lithium 3475 mAh 3430 mAh 3235 mAh
Tenergy AA Premium NiMH 2618 mAh 2577 mAh 2485 mAh

 

Unfortunately, the only reliable way to measure the remaining capacity of a battery is to run the above tests, but in the case of the Alkaline and Lithium batteries, that will discharge them to a non-usable state. We have worked with an engineer at Energizer and we both have concluded this statement is true. Are there other ways of testing a battery without discharging it to a non-usable state? You could check the voltage of a battery with a multimeter, but it is not a good test of the remaining capacity or condition of a battery as they do not place a significant load on the battery when taking a voltage reading. A battery might have a voltage reading 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 made battery testers that perform the test by placing a load on the battery for a few seconds and then a voltage is read. This voltage is compared to predetermined values from a discharge graph to turn on a certain number of LED's or bars in a graph display. These types of testers do an adequate job on alkaline batteries, as the discharge graph has enough slope to it that allows for a good prediction of the capacity. But, for Lithium and Nimh, the discharge graph is so flat that the voltage stays reasonably constant throughout the discharge cycle, thus making a prediction of the capacity unreliable. Most trail cameras have a battery meter displayed on the LCD screen and would function about 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 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. What will be the 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 many 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