Let’s talk Trail Camera batteries… (Part One)


      If you’re like most first time trail camera users, you’re at risk for being overwhelmed by the technology involved.  You spend countless hours researching and testing and just when you think you’ve got it figured out, you stumble across the subject of “batteries”.  It seems simple enough.  Pop a couple of Duracell's in, and you’re done… Right?  Well, maybe.  I guess we would first have to ask, “Which type of Duracell batteries did you install?”  Standard alkalines, NiMh rechargeables or lithiums?  And, what kind of climate are you placing your cameras?  And, and, and…and it gets a little more complicated.

      So, lets talk about the three main types of batteries, their characteristics, and why you might want to use one type over another.


Nickel Metal Hydride (Nimh) Rechargeable Batteries


Why You Should Choose Nimh Batteries
  • Less expensive in the long run
  • Longer battery life in winter months
  • "Earth Friendly"


     NiMh rechargeable batteries were introduced as the successor to Nickel Cadmium (Ni-cad) rechargeable batteries.  As you may recall, Ni-cad batteries were widely criticized for developing “Memory”.

     If Ni-cad batteries were used and not drained completely, they would often lose a portion of their capacity.  In contrast, once Nimh batteries have been conditioned (Fully discharged through 2-3 charging cycles) they can be charged at any point in the usage curve with no fear of memory development.

     Fully charged, Nimh batteries produce about 1.4 volts.  However, they quickly decrease to a working level of 1.2 volts, which they are consistently able to deliver for the rest of the usage cycle.  However, the 1.2 working voltage does present a problem for use in some cameras.  Most cameras are designed around a 1.5 volt/cell scenario.  It is very common for a camera to use 4 batteries, or essentially a 6-volt system (4 X 1.5volts).  Many of these 6-volt systems constantly monitor the voltage and automatically shut the camera off when the voltage dips to around the 5-volt level.  With Nimh batteries providing just 1.2 volts/cell, they produce an aggregate voltage of only 4.8 volts.  This makes Nimh batteries incompatible with several models manufactured prior to 2011. Fortunately, almost all current production models have a shut off voltage of about 1 volt per cell and are compatible with Nimh batteries.
   

What we've learned about Nimh Batteries over the last decade:
 
All Nimh Batteries are not created equal
Many people have had bad experiences with rechargeable batteries.  Often times we talk to someone who has unknowingly purchased older/low capacity batteries and found the battery life to be extremely poor.  Most widely available rechargeable batteries (think discount store) have small miliamp hour (mah) capacities (1200 - 1600).  These discount store batteries seldom perform as well as alkaline batteries and usually convince the user they aren't worth the trouble.  Conversely, quality Nimh batteries produce 2500 mah of capacity (sometimes more) and outperform the best alkaline batteries by up to 50%.  Please make sure to check the Mah capacity of a rechargeable battery before you purchase.

Charging is Critical
We have learned What you use to charge your batteries has now become just as important, if not more important, than how and when you charge your batteries.  Most inexpensive chargers (think discount store again) charge batteries with a constant level of charge (200 ma) for a set amount of time (8 hours) regardless of how much capacity is remaining in the battery.  This would be fine if all of your batteries were fully drained every time you placed them in the charger, but this isn't reality.  Typically, when I run cameras I come back to the office with a box full of batteries and no idea how much capacity is left in each cell. Luckily, we use a smart charger with a microprocessor which individually monitors the charging of each cell based on the cell's remaining capacity. The smart charger brings each cell up to a full charge (independent of the other cells) and then switches it over to a trickle charge for storage until it's pulled from the charger. Conversely, cheap chargers apply the same amount of charge to all cells and often overcharge batteries.  Batteries exposed to a greater level of charge overheat and lose a portion of their future capacity - some even fail immediately.  If you want to fully enjoy the benefits and efficiencies of Nimh batteries, please use a smart charger.

Put your batteries in use the instant they are removed from the charger
Nimh batteries begin to self discharge immediately after removal from the charger, even if they aren't being used.  Each cell loses about 1/2% of its capacity each day until it is completely drained. In order to maximize battery life, plan trips to your scouting area and charge accordingly.  When put into the field immediately, we get 2 - 2 1/2 months of battery life from our Nimh batteries.

Set realistic life expectancies for your batteries
Manufacturers of rechargeable batteries make claims of "Hundreds" if not "Thousands" of possible recharges. I'm sure this is possible when used in a high energy device which requires daily charging.  However, based on our experience, we expect somewhere between 3-5 years of field use from our Nimh batteries. 

Avoid using Nimh batteries during periods of high heat
We've noticed a sharp decline in battery life when temperatures rise above 90 degrees.  In fact, during a stretch of 100 degree days we noticed batteries which normally lasted 10 weeks only surviving for a week or two.  When Nimh batteries suffer, alkaline batteries perform great.  We make a point to switch out our nimh batteries with inexpensive alkaline cells during the hottest months of the summer.

 


Alkaline Batteries


     Alkaline batteries are certainly the most widely available and least expensive, but are not without drawbacks.  Alkaline batteries are shipped with a power level of about 1.6 volts, but begin to decrease in power the instant they are inserted.

     As time goes on, the voltage level continues to decrease proportionally to the time left in the field/number of photos taken.  This proportional decrease is especially evident when you examine night photos taken by infrared cameras.  Photos taken early in the life cycle of an alkaline battery are bright and well illuminated.  These early photos also represent the maximum flash range potential of the camera.  However, with every passing day each subsequent night photo will be less illuminated.

     The process will continue up until the point where night photos are pitch black and/or the camera shuts off due to low voltage.   In addition, cold temperatures adversely affect alkaline batteries.  Battery life is diminished and alkaline's lose up to half their capacity in sub-freezing weather.

     Finally, alkaline batteries are good for only 1 use and then find their way to the landfill. Most environmentally conscious people avoid the use of alkaline batteries whenever possible. 


     To summarize, alkaline batteries are cheap and available everywhere, but provide inconsistent power and don’t work well in the cold.


Lithium Batteries


      Lithium batteries offer some very interesting benefits.  To start, lithium batteries produce 1.8 volts/cell, or as we like to say “They run hot”.  Just as decreasing voltage produces weaker flash characteristics, increased voltage produces a stronger flash with brighter pictures.

     We are noticing about a 10% increase in flash range when using lithium bats.  In addition, starting out with the higher 1.8 voltage is like installing an auxiliary gas tank in your vehicle.  Lithium batteries will increase the amount of time your camera can stay in the field.

     Due to their chemical make up, lithiums are also not effected by cold weather.  One aspect of lithium batteries that can be interpreted differently is they are currently only available in AA’s.  For anyone who operates a “D cell” based camera, you’re out of luck.  However, if your trail camera requires “C” cells you can benefit from the extra voltage lithiums offer.  Fortunately, AA’s and C’s measure exactly the same from tip to tip.  Inserting “AA” lithiums into aftermarket sleeves brings the overall diameter up to that of a “C” cell and makes for a perfect substitution.

     Another benefit of using the AA’s is they are substantially lighter, and take up far less space than the larger “C” cells.   If you’re backpacking in to change out several cameras this is very advantageous.  The downside is lithiums are quite a bit more expensive, and just like alkalines, they are also headed for the landfill after only 1 use.


Batteries (Part Two)

Battery Life


      Of all the tests we complete, Battery life is without a doubt the most complicated.  With so many variables contributing to the ultimate outcome it can become very confusing.  The best way to start the discussion is to identify each variable we test, and then explain how that variable relates to other variables and ultimately determines the overall battery life of a particular scouting camera. 

Current Draw (resting power consumption)

      Every trail camera requires a certain amount of energy to keep it alive and alert waiting for the next animal to walk by.  Resting power consumption values range from as little as just .17 milliamps (170 micro amps) up to a whopping 11 milliamps or more.  At Trailcampro we measure the resting current draw of every game camera we test and then compare it to the milliamp hour (Mah) capacity of the camera’s power supply (batteries).  Simply defined milliamp hour capacity is the maximum load (expressed in milliamps) which a battery can sustain for one hour. A great analogy to Mah capacity would be the volume of gasoline which a particular car’s gas tank is capable of holding.  And just as we can calculate the range of any vehicle based on the size of its gas tank and corresponding mpg, we can also extrapolate the maximum number of days a camera can last in the field by dividing a trail camera’s resting current draw into the mah capacity of its power supply.  Please note I said “maximum” number of days because this calculation doesn’t consider other variables such as number of pictures taken, ratio of night vs. day photos, self discharge rate of batteries, net power consumption used per each photo, etc, etc.  However, for simplicity’s sake, we can calculate the total number of days a camera can last in the field without taking any pictures as follows:

      (MAH capacity/resting current draw)/24 = number of days in field before running out of battery power

A real life illustration of this is demonstrated by comparing the two models below:

Reconyx HC500
Battery Type 12 AA’s producing 5000 Mah @ 9 volts
.22 milliamp resting current draw
(5000/.22)/24= 947 maximum number of days in the field

Stealth Cam Archer’s Choice
Battery Type 8 AA’s producing 5000 Mah @ 6 volts
3.97 milliamp resting current draw
(5000/3.97)/24= 52 maximum number of days in the field

      As you can see, the differences can be quite dramatic.  In the above example the HC500 has the potential to last in the field for nearly 2 1/2 years while the Archer’s choice can’t make it 2 months.  Now, there is quite a difference in price between these two units with the Reconyx costing nearly 3 times as much as the Stealth.  However, when you factor in the cost of batteries over the course of the camera’s useful life, the discrepancy in price might become negligible. Energy efficiency should clearly play a significant role in your choice of a trail camera.

Photo Power Consumption

      From the instant a scouting camera first detects motion a whole series of events take place while the system completes the process of capturing and storing a photo.  This series of events varies in duration, scope and intensity depending on the brand and model of game camera. Some of the more common activities include, but are not limited to:

•    Sampling available light & adjusting exposure settings for optimum photo quality
•    Taking a sample photo or two
•    Charging the capacitor which powers the incandescent flash
•    Diverting power to the infrared flash
•    Accessing the storage device to prepare it for writing the photo to memory
•    Capturing the photo
•    Storing the photo to memory
•    Accessing instructions from the firmware to determine how and when the next photo should be taken

      All of the above functions require time and consume power.  While some manufacturers complete these tasks with great efficiency, others struggle.  Photo power consumption values range from just 140 milliamps for 1/2 second up to surges of over 1000 milliamps with increased power lasting well over 60 seconds.  By meticulously measuring this data we can quantify the power required to process a photo in every camera we test.  We can then calculate the maximum number of photos a scouting camera is capable of capturing on a single set of batteries.  In addition, further computation provides us a quantifiable loss of time in the field each photo robs from the camera’s standby time in the field.  An example using the Moultrie M100 would be as follows:

•    The Moultrie M100 has a resting (standby) current of.17 milliamps
•    When the M100 takes a photo it draws an average of 170 milliamps for a duration of 18 seconds
•    If we calculate the total amount of power used to capture the photo, we come up with 3060 milliamp seconds (170 milliamps X 18 seconds)
•    To determine the amount of standby time lost from the power consumption required by a single photo we simply divide the resting current draw into the total power consumed by a photo and then convert from seconds to minutes to hours(((3060/.17)/60)/60)=5
•    By calculation, each photo taken decreases the amount of time a M100 can last in the field by 5 hours

      This may or may not seem relevant or important, but for practical purposes every 5 photos taken by a M100 costs you a day of standby time in the field.  For comparison’s sake, a Reconyx HC500 placed in this same scenario could take 266 daytime photos before it used up a day’s worth of standby time.

      You’ll find values for power consumption and time lost in the field for every camera we test.

      Shut off voltage (minimum level of voltage required to power camera)

Another item we test is “Shut Off” voltage. Simply put, a scouting camera’s shut off voltage is the minimum level of volts required to power the camera for normal operation.  Anything less and the camera will shut off due to insufficient power.  While rarely mentioned, this particular attribute becomes relevant in many ways. To fully understand, we must first explain how batteries perform throughout their lifecycle. The graph below illustrates how the voltage in different types of batteries decreases over their lifecycle.



     
You’ll notice alkaline batteries start at 1.6 volts and then immediately begin a gradual decline throughout their life until they are “dead”.  However, Lithium & Nimh batteries maintain a steady level of voltage (albeit different levels) throughout most their life and then completely die all at once at the end of their life.  When combined with the shut off value of a particular scouting camera, the usage curve of each type of battery becomes important in two (2) key areas:

1.    Some game cameras are incompatible with certain types of batteries due to their shut off values (minimum power requirement). Most camera manufacturers design their cameras using a 6 volt power supply (4 batteries at 1.5 volts each = 6 volts).  Many of these same manufacturers also program in a shut off voltage of about 5 volts. It is this 5 volt shut off threshold which creates a problem for anyone wanting to use Nickel metal hydride (Nimh) rechargeable batteries.  Nimh cells provide consistent power and aren’t affected by cold temperatures like alkaline batteries which can easily lose up to half of their capacity during sub freezing weather.  They are also very economical given they can be used for hundreds of charging cycles.  However, Nimh batteries have a working voltage of just 1.2 volts/cell or 4.8 volts aggregate when used in the typical trail camera. Unfortunately, anyone who owns a scouting camera with a shut off value above 4.8 volts can’t benefit from the advantages of Nimh batteries.  In our Battery Life spreadsheet we document the shut off value for all cameras tested & specifically highlight those which are not compatible with Nimh batteries.
2.    Some Trail Cameras are incapable of utilizing the full mah capacity each battery offers.  Using the graph above from the previous example, you’ll notice the voltage in alkaline batteries dips to about 1.2 volts one fifth of the way through its usage cycle. At this point the aggregate voltage in many game cameras has dropped below the shut off threshold forcing the unit to shut off leaving the camera’s batteries with 80% of their capacity unused.  Getting back to our automobile gas tank analogy, this would be equivalent to providing a 20 gallon tank with a fuel line which only reached down far enough to access the top 4 gallons.  This issue only applies to the use of alkaline batteries.  Lithium cells provide adequate voltage throughout their entire life cycle and Nimh batteries shouldn’t be used in any camera with a high shut off voltage. 


Conclusion

      As you can see, the variables involved with battery life (many of which are not constant) make its calculation anything but an exact science.  However, what we can determine with great accuracy is the power consumption associated with each model.  We can then plug those figures into a formula and produce battery life estimates.  While these estimates may not be exact for each model, the relationship or ranking of one model relative to another is.  So, while we cannot say the battery life of a Reconyx HC500 is exactly 234 days, we can say that a Reconyx HC500 will last about 10 times as long as a Stealth Cam Archer’s Choice model on a single set of batteries.