Decide on battery type for outdoor project.   - Page 1
Forum section: electronics / projects

author: viper
author_rank: Regular Contributor
timestamp: August 07, 2025, 09:50:57 pm
content: I'm looking to use battery power to power a sensor system and ESP32 module. The all equipment will need to survive the elements. I am designing around extremes of both hot and cold. The battery power would be designed to supply many days of operation without charging. Actually potentially 30 days but I'm looking for maybe a set and forget type deal. I was primarily focused on an 18650 or a pair if needed. I was considering a small solar cell for charging but I know many of the chemistries need extremely careful charging at high temps, and refuse charging at low temps. In extreme cold, I was even considering just burying a battery case to protect it, but don't want to go that route if not needed.Are there any other battery options I might consider? I was planning to use the onboard temp sensor on the ESP to decide on charging.

author: Benta
author_rank: Super Contributor
timestamp: August 07, 2025, 09:55:54 pm
content: Info on current draw would be helpful.

author: viper
author_rank: Regular Contributor
timestamp: August 07, 2025, 10:19:15 pm
content: Quote from: Benta on August 07, 2025, 09:55:54 pmGets deep but a work in progress. Basically Will stay in a certain state of sleep, est 1-3mA. When active, will send and receive sensor signals approx 1x/min for about 2hrs a day. Peak current during most active modes est about 1A. Oh, should mention, when active, the event that pulls the max 1A current happens for only about 2 seconds for each 1min reading. Hope that is in someway clear.

author: Benta
author_rank: Super Contributor
timestamp: August 07, 2025, 10:37:34 pm
content: How about solar cell + supercap and alkalines for the night? Cheap and easy.The supercap would take care of the high-current periods (seconds?).

author: viper
author_rank: Regular Contributor
timestamp: August 07, 2025, 11:10:50 pm
content: Quote from: Benta on August 07, 2025, 10:37:34 pmIs 1A really enough to get a benefit from a super cap? I haven't reviewed them in years to know how much they can hold.I was also thinking if I should just be more sensible and consider a battery door and just plan to do separate charging of the 18650, or even a pair of them.Reality here is there will be power available as 120-240V, but due to being a potentially commercial device, I would have to work the safety and possibly UL side of that.I know some of these devices would just be subjected to insanely cold temps, in which battery charging without heating may not be possible. Obviously Tesla knows that issue well.To be honest, I won't know the real power needs until the device is totally complete and a power study is concluded.

author: antenna
author_rank: Frequent Contributor
timestamp: August 07, 2025, 11:36:25 pm
content: Regular energizer lithium. -40 here in MN and the long range driveway alarm works great. I think they handle heat better than the LiPo cell phone types too.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: August 08, 2025, 01:33:30 pm
content: I agree with Antenna, the Lithium 'primary' cells work well in winter conditions, as my outdoor weather temperature & humidity sensors transmit their data into my home flawlessly, but be aware that when new,their voltage is in the 1.8 VDC range.

author: fchk
author_rank: Frequent Contributor
timestamp: August 08, 2025, 02:44:08 pm
content: Suggestion:https://saft4u.saft.com/en/download_file/faf5307b-9cfc-4b99-a1c4-d88b9dac56c9/English

author: Peabody
author_rank: Super Contributor
timestamp: August 08, 2025, 04:16:51 pm
content: There have been multiple reports of failure of Ultimate Lithium primaries. The battery voltage just drops to zero for no apparent reason.https://www.eevblog.com/forum/renewable-energy/sudden-death-problems-with-energizer-ultimate-lithium/But as long as they don't die, they would probably be the least affected by cold. If you use lithium ion, maximum current will fall in cold weather, and I think it would be best to disable charging when it's below freezing.That said, a lot of these solar garden lights that you see use NiMH cells, which seem to work well enough, but that's low current.

author: mikerj
author_rank: Super Contributor
timestamp: August 08, 2025, 04:22:50 pm
content: TheTadiran TLIseries Li-Ion cells are specifically designed for harsh environmental conditions.Lithium Titanatealso has a wide temperature range and very high cycle life, though lower energy density.

author: mariush
author_rank: Super Contributor
timestamp: August 08, 2025, 04:33:17 pm
content: LiFePO4 are supposedly rated for down to -25c and can be trickle charged with 3.6v or lower (per cell)See for examplehttps://www.digikey.com/short/v5b4jrp4The 18650 cells from zeus are advertised as discharge -10c to 60c :https://www.digikey.com/en/products/detail/zeus-battery-products/PCIFR18650-1500/9828824The 26650 cells from PHD energy are advertised as -20c .. 60c :https://www.digikey.com/en/products/detail/phd-energy/PHD-26650-LFP-3600/25019871Plus you can get them in 14500 size (similar size to AA) so in theory you could put a bunch of them in a AA battery holder to get higher voltage or to be able to charge them with a simple regulator from a higher voltage solar panel.ps you could go big and get a 12v lifepo4 battery similar to lead acid batteries exhttps://www.digikey.com/en/products/detail/nppower-international-inc/LITHIUM-12-8V12AH/21676566or flat batteries likehttps://www.digikey.com/en/products/detail/power-sonic-corporation/PSL-FP-IFP2770180EC/13577480

author: viper
author_rank: Regular Contributor
timestamp: August 08, 2025, 10:17:03 pm
content: Here is sort of where I'm at. Solar charging just seems like the right approach. I think I just need to design around having enough battery capacity when temps are not acceptable for charging. I thought about deploying any spare solar to heating, which I guess could work, but adding in complexity.I might ask the question in terms of price or advantages, are Lipo type packs our pouches more economical than the metallic cells? I commonly see them in RC applications and they have a built in temp sensor. Thinking that might be a better strategy.I am trying to keep this as much 'set and forget' as possible.

author: mikerj
author_rank: Super Contributor
timestamp: August 09, 2025, 10:47:07 am
content: There may be some specialist cells available, but regular pouch cells as used in RC etc. use NMC chemistry for high energy density and are not rated for wide temperature extremes. This is particularly true for charging, where charging below freezing (0C) can cause internal damage to the cells.

author: viper
author_rank: Regular Contributor
timestamp: August 09, 2025, 03:42:34 pm
content: Through a range of studying, what I am leaning towards is a LiFePO4 cell. A single cell with boost converter. No balancing, and seems LFP may be more tolerant to temp extremes than Ion. I would just have to inhibit charging in extreme cold. With at least some energy calcs, it looks like a battery can last at least 30 days and some calcs showing a year.Since I sort of want to monitor and report the battery life via wifi, I know I will have to get into coulomb type strategies as LFP SOC is extremely flat so just looking at voltage alone won't work. But the way I might approach is know that once voltage starts to rise on the curve, I can then predict where I am at in SOC and start the counting, or reset the counting if that makes sense. It doesn't have to be insane accurate, but a decent idea.

author: Peabody
author_rank: Super Contributor
timestamp: August 09, 2025, 04:01:36 pm
content: What will awaken the circuit? If you have a switching regulator, it will tend to be less efficient during sleep. So depending on the sleep pattern, it might significantly extend battery life if you can power down everything but the charger during sleep. But then you'd need something to turn the power back on, like an RTC running on its own coin cell.

author: viper
author_rank: Regular Contributor
timestamp: August 09, 2025, 05:57:51 pm
content: Quote from: Peabody on August 09, 2025, 04:01:36 pmHonestly haven't got that far yet. If it brings a distinct advantage, I could do a 2S LFP setup to keep voltage higher, but of course would then need a little BMS. I guess my thought in the design was to get enough Wh in the design, plus charging so I didn't have to chase extremes with power usage.

author: whollender
author_rank: Regular Contributor
timestamp: August 09, 2025, 09:30:55 pm
content: I recently made a Lora water level sensor that has to live outside in central Montana.We occasionally get high temperatures above 100F in the summer and can spend weeks below freezing in the winter.I started with a small lipo battery and solar charger from ada fruit, but then discovered that charging at low temperatures can cause permanent damage.I know that lithium batteries can theoretically be trickle charged below freezing without forming dendrites, but I'm not willing to risk the possibility of starting a grass fire out here on the prairie. And not charging below 32f is just not really a practical solution for something that I want to have nearly 100% uptime.I ended up just getting a small lead acid battery that's designed for lawn mowers. It has way more capacity than I need, but it's inexpensive, much more resilient to low temperatures, and solar chargers are very easy to find.