# Simple and inexpensive battery heating and cooling in a harsh environment?

What are your recommendations for methods or devices that are neither complex nor expensive to keep batteries warm and cool in a harsh (hot/cold/moist/dusty) environment, to ensure long cell life?

I'm designing a small solar-powered camera product and I have my choice of battery types: lithium, lead, nickel, etc. The camera would sleep most of the time so for average hourly use I estimate around 10mA x 12V (120mW). The environment could be very dusty, humid, hot, or cold. I cannot require constant maintenance, so a fan with filter does not seem to be a good idea. I can go with a larger pack to reduce the charge/discharge rate, if that is necessary.

Since this is for the outdoors and the initial sales would be in the United States, I expect ambient charging temperatures to be between -18°C/0°F in the winter and 38°C/100°F in the summer. Discharge temperatures could be as low as -34°C/-30°F in the winter and 38°C/100°F in the summer. Humidity can be as much as 100% but 87% is more typical in locations like Florida or Louisiana.

I was asked to supply the following info:

• How your device looks: Imagine a security camera with a solar panel.
• What it might cost: Less than USD $100 with parts cost less than$50 would be ideal. Any more than that and I might not consider creating the product.
• What amount of field failure you can tolerate: Not sure how to quantify this. A life of 5 years would be fantastic. No less than 3 years.
• Where it's going to be mounted by whom: Eaves, trees, walls, by non-trained personnel e.g. homeowners, farmers.
• How heavy it might become: Small device, so about 1-2kg/2-4lb.

Is this even a concern? On my house I have these solar-powered security lights that have no heating or cooling. Just Ni-Cd batteries in a black plastic enclosure. I live in a climate with hot summers and cool winters. The devices are mounted in the sun and have been going strong for years. I see from reviews on those devices that they are installed in both very cold and very hot locations, and perform admirably. Yet the typically-recommended charge/discharge temperatures for Ni-Cd cells is 0°C to 45°C and -20°C to 65°C, respectively. Cells in an uninsulated black plastic box exposed to sun and snow surely must reach temperatures outside of that range, right?

And there are solar-powered trail cameras that hunters use in cold and hot weather.

Am I over-thinking this? Should I just drop some Ni-Cds in a black plastic enclosure and be done with it? Or are there some inexpensive temperature management solutions?

• can you define "hot", "cold", "humid"? – Marcus Müller Sep 3 '17 at 11:59
• Snow, dust, mold, dead leaves on solar panels can be an issue. Also, if you want to keep the electronics cool in the summer, keep them away from direct sunlight. – bobflux Sep 3 '17 at 12:07
• @MarcusMüller apologies, I thought that would be self-evident in the question since it is for an outdoors device. I have updated the question to reflect my expectations for temperature and humidity. – SlowBro Sep 3 '17 at 12:15
• These expectations are realistic for moderate climates. For a camera in southern Sahara, or Antarctica, these wouldn't be sufficient :) But that's why I asked, thanks! – Marcus Müller Sep 3 '17 at 12:17
• Minus 20 Celsius is a tad below what northern USA might expect. I had to design a battery powered piece of kit for Chicago and minus 30 was the spec. But this site isn't for developing a spec and seeking product recommendations is also off topic so, with a pun in mind, you are skating on thin ice. – Andy aka Sep 3 '17 at 14:46