# Maintain voltage and current supply to device in extreme cold

I am running a DSLR to take time lapse photos for long periods of time, often overnight, often in extreme cold (-20F). If at any point the camera does not get enough power, it shuts down - time lapse over. The stock lithium batteries I believe are rated 7.2 or 7.4 volts but measure 8.4v when fully charged.

I have been using a 12v 12AH SLA battery connected to a voltage regulator (DROK DC-DC 6-32V to 0.8-28V 150W 15A) to output 8.4v. This works well but fails in the coldest of temperatures.

If I am losing camera power, is it likely because battery voltage is dropping in the cold? Meaning I should wire two batteries in series increasing voltage before the regulator and allowing the voltage to be maintained at 8.4v?

Or is current dropping because of the cold and I should put them in parallel? Or both?

• Are you using any insulation for the SLA battery? Otherwise you might just get away with better insulation. Jun 3 '19 at 8:47
• In the space industry the solution is simple: heaters that drain some of the current to keep the batteries sufficiently warm.
– SF.
Jan 27 '20 at 10:40
• +1 for actually posting units of temperature instead of just saying degrees and assuming everyone uses F and leaving the rest of us to try and guess Jan 21 '21 at 14:36
• Do you ever record longer than overnight? If so, insulation and battery powered heaters may not be enough and you may need a electrically ignited and electromechanically snuffed chemical fuel like food warmers, but that is hardcore. Your camera doesn't suffer at those temperatures? Jan 21 '21 at 14:39
• Or heatpacks for shipping animals with insulation. But 20 - \$30 a pop for 72h packs: amazon.ca/72-hour-Uniheat-Shipping-Reptiles-Tropical/dp/… Jan 21 '21 at 14:42

Based on the extremely low temperature you've described, it's likely the temperature is causing the drop-out of your system.

According to All About Lead Acid Batteries, the voltage you read at lower temperatures is not accurate. The voltage shown on the meter will by higher than reality. The chart shows that at zero degrees F, a battery that reads 12.082 volts is effectively fully discharged. Extrapolating from the chart, at minus twenty degrees F, your battery is dead even though it might display 12.14 volts. For high current draws, it is inadvisable to discharge a lead acid battery below fifty percent depth of discharge, as it results in reduced battery life. At lower current levels (your application) going below twenty five percent state of charge will also reduce life span.

According to Thoughtco.com, as the temperature drops, the current available also is reduced. Especially in lead-acid batteries, this turns the Peukert effect into a fairly detrimental situation. Your device requires more current, the lower temperature reduces the current, causing the device to "demand" more, which likely drops the voltage, increasing the current demand. It's a downward spiral.

You could consider alternative options. Dedicate a battery to a low wattage heater that will keep the primary battery warm. Especially insulate the enclosures for the battery or batteries. With the low temperatures involved, a fairly large expanded polystyrene cooler with thick walls (more than one!) nested together could give you the thermal stability required to complete the tasks.

Connecting batteries in parallel will provide more current to the device, but will still suffer from the cold temperatures.

Lithium chemistry based batteries are not to be charged at temperatures below freezing. If your camera contains such a battery and the supply voltage is at a charging level, you may be damaging the internal battery as well. These batteries also suffer from reduced output and capacity in extremely low temperatures. Our EVs present a dash panel warning at low temperatures indicating that regenerative braking may be reduced. The onboard computers prevent the system from charging the pack during extreme cold, reducing the chance of damage to the pack.

Batteries depend on chemistry, and chemical reactions slow down in the cold, so any kind of batteries are always going to have poor performance in extreme cold weather. The other suggestions given so far are good. Here is an another option (depending on your budget and general familiarity with electronics). You could just ditch batteries altogether and go with supercapacitors. Supercapacitors have lower power density than batteries, but since there is no chemistry involved, performance is pretty good, even down to -40C. You do lose a little bit of performance at low temps, but nothing close to what a battery loses. It has been said that the Russian military uses supercapacitors to start their tanks in the winter in Siberia (see Ref 1) Here is one example of a commercial available supercap]1. It's fairly cheap, but only goes to about 3V so you'd have to stack a few of them together to get up to 7-8V. 3000 farads means it'll store quite a bit of energy. You'd need to do the calculations on current draw to see if that's enough to get you through the night. It won't be as much as your 12 Ah battery at room temp, but it's probably better than the battery at extreme cold.

(1) Encyclopedia of Electrochemical Power Sources edited by Jürgen Garche, Chris K. Dyer, Patrick T. Moseley, Zempachi Ogumi, David A. J. Rand, Bruno Scrosati