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I use several low-end trail cameras for monitoring wildlife. All of them are powered with 4 x 1.5 V AA batteries. Replacing non-rechargeable cells in several trail cameras starts to generate more electro-waste than I like (and it also costs money). All cams have external 6 V DC input, so I am starting to think about options I have in order to get rechargeable source of 6 V. Regarding current, it only takes few mA (maybe les than 1 mA) in stand-by and this usually takes most of the battery life.

As first, I have asked a manufacturer of my recent trail camera (Suntek Mini300) about using 7.4 V (2S li-ion cells) as external power source. As I expected, they do not recommend it, because "the infra LED will not work" (no more details to this statement). So I will probably need source of 6 V. Below, I sum options I came with. There is a need to say, all of them will be really "external" - can not be fitted to 4xAA compartment in trail camera.

  1. 5xAA Ni-MH 1.2 V cells - probably the simplest solution, but re-charging 5 cells is really uncomfortable.
  2. 4xAA Ni-MH 1.2 V cells + step-up converter - I know very little about it, but stepping up 1.2 V might not be very efficient.
  3. Li-ion 3.7 V cell / 2P cells + step-up converter - I have no experience with li-ion cells in outdoor conditions + uncertain efficiency. 1 cell might not have enough capacity, and connecting 2 cells in parallel may be dangerous.
  4. Li-ion 2S cells @ 7.4 V + step-down converter - low voltage difference -> might not be very efficient (?)
  5. Li-ion 3S cells @ 11.1 V + step-down converter - voltage difference is higher, so conversion might be more efficient(?)
  6. Above mentioned with Li-po cells - no experience, aware of cold conditions
  7. 6V Pb cell - can have enough capacity, but is too bulky & heavy and especially not very eco-friendly.
  8. Lion 2S @ 7.4 v directly :) - should I try it despite the fact it is not recommended? It is needed to assume 8.4 V when fully charged.
  9. Other suggestions?

Personally, I mostly like first 2 options, but maybe I have not mentioned some obvious solution, that is why I am asking here. I will be very grateful for any suggestions or discussion of above stated options. thank you.

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  • \$\begingroup\$ You realize that the "most energy and space efficient" solution is likely to also be the most expensive, don't you? Is that acceptable? It sounds like "eco-friendly" is important to you...can you explain what your criteria are for that? \$\endgroup\$ Apr 15 '20 at 20:19
  • \$\begingroup\$ @Elliot Of course that was needed to state in my original question, I am not willing to invest more money in battery than whole trail camera, lets say 30 €. So it should be low-cost solution :) I use cheap trail cameras because there is high risk of getting stolen. Anyway, I am still interested in your suggestion, so do not get limited by my budget. And that "eco-friendly" was maybe too hasty statement, as I do not believe that other battery types (than Pb) is more friendly to nature when damaged. \$\endgroup\$
    – Oki
    Apr 15 '20 at 20:39
  • \$\begingroup\$ Have you tried using LSD (Eneloop or equivalent) NiMH cells? \$\endgroup\$ Apr 16 '20 at 2:13
  • \$\begingroup\$ @BruceAbbott not yet, as they only supply nominal 4.8 V when 4 of them used. I believe the trail camera will operate at the beginning, but I guess as the cell will get discharged a bit (or during cold night) the operation will start to be very unreliable. Currently, all my traps are in a terrain, but I can try it in home in a few days and let know here. \$\endgroup\$
    – Oki
    Apr 16 '20 at 4:16
  • \$\begingroup\$ For the "other" category: amazon.com/Capacity-1850mAh-Blackube-Rechargeable-Batteries/dp/… They look like AA batteries, and they fit in an AA battery compartment, but each one contains a Li-ion cell, a step-down circuit that supplies a steady 1.5V to the appliance until the cell is almost depleted, and a charging circuit that lets you re-charge the cell from a USB source. I have had good luck with the AAA-size product made by this same company. Haven't personally tried their AA-size. \$\endgroup\$ Apr 16 '20 at 7:17
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You should try checking out LifePO4 batteries as an alternative solution. They have a nominal voltage of around 3.2V, so having 2 in series is 6.4V, which is really close to what your camera needs. You will require a (tiny) BMS circuit on it though since discharging them below its recommended minimum voltage will permanently damage it.

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I have actually first come across similar cameras about a month ago, possibly the same model or manufacturer.
A customer was confused as to why they worked on batteries but not on an adapter. He thought some electronics failed on the board. I discovered that the camera actually needed a specific voltage range or it wouldn't even turn on. I don't remember exactly, I think it was from 4.5V to below 9V. He actually had a power supply whose voltage was outside of this range (I think 12V).

Anyway, first to correct you: connecting 2 cells in parallel can be dangerous only if their charge levels vary greatly (like more than 0.2-0.3V I think), so all you need to do is make sure their voltages are within 0.1-0.2V of each other when connecting them together and they will just work great afterwards.
If you are using a DC-DC converter, make sure that it has a VERY low quiescent current (the amount of current it uses with no load whatsoever, for running its own circuitry).

Before trying anything else, I would suggest you measure a camera's current consumption at 5, 6, 7 and 8V and see if it varies significantly (especially with the IR LEDs turned on).
Your solution might be as simple as 2 Li-Ion cells in series, without any conversion. You would just have to make sure they disconnect before the voltage of either cell drops too low (below 3.2V; depends on its chemistry). If the cells have circuitry on them, that's good, but you may want to have your own adjustable, micro-power monitoring circuit.

One tip: lithium cells can be recharged many more times if you use only 50% of their capacity (from 30%-80% charge level), so you could employ that tactic.
Another tip: You could include a ~7.2V mini solar panel to charge your batteries. It wouldn't be much larger than the camera.

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  • \$\begingroup\$ Thank you, very informative answer. But need to clarify some points. 1. Are you suggesting to hook the camera on variable-voltage supply and try the range from 5-8V, while measuring current? Should not I be afraid of the overvoltage? I hope that both internal and external (AA bateries, DC jack) are somehow regulated, but It is just my wish. 2. I already have some protection circuits for li-ion cells. They should also protect cells against over-discharge. But I do not know If I should also use them while charging, or rather charge indiv. unprotected cells in charger. But this is off-topic. \$\endgroup\$
    – Oki
    Apr 16 '20 at 4:30
  • \$\begingroup\$ The one I looked at contains PWM DC-DC converter. If you start at 5V and slowly increase the voltage to 6V, you should notice a DECREASE in current if yours has PWM circuit as well and that means your input voltage can go from around 4.5 to around 9V. I don't remember if it has conversion on the battery side (I think it does), but it should have it on the DC input side. \$\endgroup\$ Apr 16 '20 at 7:39
  • \$\begingroup\$ As for your second question, you should use that protection circuitry both while charging and discharging, but you should check its current consumption. \$\endgroup\$ Apr 16 '20 at 7:40
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remember you get a robust 0.6 or 0.7 volts drop across silicon diodes.

consider 1n4001 for your current level

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