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Home→Blog→Camera Trapping Technology→Deep Tech→Internal and External Trail Camera Power

Internal and External Trail Camera Power

Winterberry Wildlife Posted on by

Many trail cameras support both internal batteries as well as an external power supply. When there is only one power source, it’s clear where the power comes from. But what does the camera do when both internal and external power is available? If you use rechargeable batteries inside the camera, and a set of primary batteries in an external pack, which set will the camera use first? How does the camera switch over when one source of power runs out? In this post, look at trail camera power in the Browning Recon Force Advantage (BTC-7A camera). I give guidelines on different options for internal and external battery types, as well as external solar-battery power supplies. These results apply to other trail camera models, as well, since they share similar power supply architectures.

use of internal and external power in trail cameras
Lab setup for determining how a Browning Recon Force Advantage (BTC-7A) consumes power from internal batteries and an external source. I have used a variable power supply (on the left) to emulate the internal batteries; and a second power supply (not shown) to provide external power through the adapter in black.

Summary

Technical details for this post are below. Based on this data, here is a quick practical guide to trail camera power.

Same Battery Types

If you use the same type of batteries with the same initial charge internally as externally, they will be discharged equally. For example, if you use AA LiFeS2 (E.g. Energizer Ultimate Lithium) for internal and external power, all 16 batteries will have the same charge left when you service the camera. A set of the sme type of batteries with more charge (higher voltage) will be used preferentially until the two sets have equal remaining charge.

Different Battery Types

If you use different types of batteries, the ones with the higher nominal voltage will tend to discharge first. The table below summarizes trail camera power when using different types of batteries internally and externally.

Internal BatteryExternal BatteryFirst to Discharge
NiMH (8 batteries at ~9,.6V)LiFeS2 (8 cells, 13.2 Volts)
Li-Ion AA (8 cells, 12 Volts)		External
Li-ion AA (8 cells, 12 Volts)LiFeS2 (8 cells, 13.2 Volts)External
LiFeS2 (8 cells, 13.2 Volts)
Li-Ion AA (8 cells, 12 Volts)		NiMH (8 batteries at ~9,.6V)Internal
LiFeS2 (8 cells, 13.2 Volts)Li-ion AA (8 cells, 12 Volts)Internal
Table showing mixes of battery types for internal and external batteries, and which will tend to discharge first

Note that some NiMH cells have relatively high “self-discharge” rates — i.e. they lose capacity over time even if they are not being used. In the scenario above, the NiMH cells may need to be periodically recharged even though the power for the camera comes exclusively from the higher voltage battery pack.

Solar Collector

The desired behavior (IMO), when using an external solar collector, is to rely on the solar collector, and its associated relatively low capacity rechargeable batteries whenever it is available. Ideally, the internal batteries would only be used for backup — i.e. to cover long stretches of cloudy weather and/or lots of camera activity. There are two ways to make this happen:

  1. Use LiFeS2 cells as internal batteries, but replacing one of the 8 batteries in the tray with a “short circuit dummy battery”. This reduces the voltage of the battery pack enough that the external solar charger will be preferred by the camera’s power controller. You can find the required “dummy AA cell”, for example, here.
  2. Use NiMH as internal batteries. Since these batteries operate a lower voltage, the external solar charger will be used.

I prefer the first option — using 7 LiFeS2 (e.g. Energizer Ultimate Lithium) batteries as the internal batteries. With its long shelf life, high reliability, and excellent cold weather performance, LiFeS2 batteries make a much better choice than NiMH cells for backup application.

Trail Camera Power: Experimental Setup

I used two variable power supplies. The first is connected to the internal battery contacts. The second to the external power plug on the camera. I then swept through a series of different voltages for each. Voltage values range from 13.6 Volts (equivalent to fully charged LiFeS2 batteries) and 8 Volts (equivalent to basically dead NiMH batteries). By measuring the current from each of the power sources, I was able to determine which was powering the camera.

This experiment measures the behavior of a specific Browning trail camera model (the BTC-7A). Other Browning models are likely to to behave similarly. Read my post on different battery types at Trail Camera Batteries: Internal AA-Cell Options for more detail on the batteries themselves.

Experimental Results

I found that if the voltage from the external power supply exceeds the voltage of the internal battery by ~0.3 Volts, then all of the current for the camera comes from the external power supply. Conversely, if the battery voltage exceeds the external power supply by ~0.3 Volts, all of the current for the camera comes from the internal battery. In the range between these limits, where battery and external power supply voltages are within plus or minus 0.3 Volts of each other, current is shared between the two — equally when voltages are equal. If they are not equal, more current is drawn from the power supply with the higher voltage. The diagram below shows a visual representation of power allocation.

Trail camera battery external power transfer function
Diagram showing trail camera power source for Browning Recon Force Advantage (BTC-7A) with both internal batteries, and an external power supply. Y-axis shows voltage of external power supply; X-axis shows battery voltage. If battery voltage is greater than external voltage by about 0.3V, all power comes from the battery (blue region). Conversely, if external voltage is greater than battery voltage by about 0.3V, all power comes from the external adapter (orange region). Where voltages are within 0.3 V, power is split between the two (green region).

Note that this camera does not include a battery charge controller. These cameras will not charge internal NiMH or Li-Ion AA batteries from external power under any circumstances.

Battery Meter

I also looked at the “battery meter” spot on the screen during these tests. This region in the lower left of the home screen either displays “EXT” (for External power source), or a bar graph and percentage of battery remaining. I found this display to be an unreliable indicator of where the camera is getting its power. In some cases “EXT” is displayed, even though all of the power is coming from the internal batteries. On the flip side, when a battery percentage is shown, I found that the camera is getting power from the internal battery.

Acknowledgements

I would like to thank subscriber KeithC for suggesting this topic.

If you have questions on this post, or any other to camera trap technology, let me know in comments below.

Comments

Internal and External Trail Camera Power — 16 Comments

  1. Awesome topic Thank you. I learned more stuff. I thought the external will always be doing the work until it discharges and then the internal will take over.

    Reply ↓

  2. Excellent review. I recently set out two camera traps with Browning External power packs. I was curious as to how the camera would use the batteries. I used Lithium in both the trail camera and power packs. Now to see how long they make it through the winter. Of course many variables with this.

    Appreciate your expertise in TC;s ” Under The Hood ”
    Jim

    Reply ↓

  3. I wish I had found you sooner, Bob!
    Everything you added to the HP5 menu was on my wishlist.
    I do have a question. Because of the power draw on the HP5
    I have been using 12v agm batteries on each cam. I charge these to around 13v. Will this harm the camera? What do you recommend?

    Thanks,
    Tom

    Reply ↓

    • I’m glad you foudn us — better late than never.

      As far as the voltage on external batteries for the HP5 (and similar Browning cameras, at least). The short answer is that you should be fine at 13 Volts. The long answer is that I have not tested the maximum voltage for the power converter. That is, I’ve not tested it to failure. However, I have routinely run it up to 14.4 Volts without issue. A set of new Lithium Metal batteries produces up to 14.4 Volts, and this is a design point for the camera. There is likely some margin above that. How much, I don’t know. But 13 Volts is fine.

      Reply ↓

  4. I have a large number of Browning cameras in the field and have switched to 12v AGM batteries mounted in small waterproof plastic ammo boxes. I charge mine to over 13V, and I have had no problems with my BTC 7E HP5, 7A, and 7E cameras. Typical recharge times are in the 2-3 hour range depending on discharge rates. I do keep a set of fully charged alkaline batteries as back up in the cams. Time in the field before recharge averages to about 2 months. I carry a multi-meter with me and note the state of charge when collecting SD cards. So far this is working for me.

    Reply ↓

  5. I am new to the solar charger and battery that comes with it,can you leave the batteries in the trail cam while you are using the solar set up? Thanks

    Reply ↓

    • Yes. These batteries will not be charged by the solar charger. Depending on the solar charger, the internal batteries may be used even though there is solar power. If this is the case, just remove them (and save yourself the cost of replacing).

      Reply ↓

    • Yes, and yes. I use a 12V external power supply by itself (empty battery tray) all the time. The only difference is the battery meter is replaced by the string “EXT”, indicating it is connected to External power. (Things only get complicated when you use an external power supply *and* internal batteries, as in this post )

      Reply ↓

  7. Hi Bob,

    Do you, or any of your readers have found a secure way to mount an external 12V battery and have it connected to a fixed trail camera in the field? Specifically, an external battery that is bear and rodent proof? I don’t know if anything could be grizzly proof, but at least black bear proof. I’ve been giving this some thought lately to save cost AND to have a camera trap site that can make it through winter, without me having to change the batteries.

    Also, do you have an opinion if a 12V.8V, 7Ah battery would have powered a Recon Force Advantage camera through a winter with your average set you and Janet would have had in Massachusetts? Nothing too fancy, just a regular trail camera set to take 20 second videos, say with the converted white flash on a fisher stump, for example. No secondary lights.

    And just out of curiosity, have you (or any of your readers) had a grizzly bear pull on one of browning cameras in a security box? How did the camera survive the encounter?

    I know black bears are curious and do this often but have no idea what grizzlies do.

    Thank you

    Reply ↓

    • I can’t do any better than the excellent overview of the external battery system given by Tom Arma a couple of comments earlier on this post.

      For reference, a 12V 7Ah battery has about 2x the capacity as a new set of 8 EULs. This would give you 26 hours of daylight video; or 8 hours of total night-time video. Tom notes that he wishes he had gotten a 10Ah version. This would give you about 3x the capacity of a new set of EULS (39 hours of daylight video; or 12 hours of night-time video. To take advantage of these long record times, make sure to use a 512 GB card!

      This said, a camera set on a fisher stump during the winter is unlikely to get very many false triggers. Under these circumstances, we never nearly approached the 13 hours of daylight video (4 hours of night time video) you get from a set of EULs, of animal action at the target over a single winter season.

      We’ve not, yet, had any our cameras attacked or even much bothered by Grizzly bears. Grizzly bears reading this — this is not a challenge! 🙂

      Reply ↓

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