Agree with the differences between microSD cards. I tested Sandisk Ultra, Samsung EVOplus, and some no-name cards I found myself in possession of. Unfortunately I did not have a logging device, but I watched what was happening on my multimeter. The µMoth with an Ultra was peaking at over double the current flow of the EVOplus. The no-name card was peaking at about the same as the EVOplus but had a near constant background drain that was not obvious with the other cards.

Apparently, cards of different sizes also use different amounts of power:

It would be great if someone with a data-logging multimeter could conduct a search to find the most power miserly cards out there, but it would be a constant search as card specifications are changing all the time. The Samsung EVOplus cards are no longer available, but I have no idea if Samsung has redesigned their cards or just rebranded them. Often manufacturers are going for the highest speeds rather than the most efficient card because most devices are using more power on sensors, screens, etc. so you barely notice a bit of surplus power going to the card.

I recently completed a survey using SongMeter minis and most units managed two weeks of nocturnal recording using eneloops and sandisk cards. But I had a couple of units that had only managed for or five nights so I redeployed with fresh batteries assuming we must have had some badly charged cells. After a week I went back to collect the units only to discover they had again gone for less than a week so this time I had some spare SM minis so I swapped the same cards into those with fresh batteries and redeployed again. After another week I went back and the same issue. We had sufficient data by now so I did not redeploy again but I concluded it was something about the SD cards that was causing the problem all along. If they were mine I would have tested them, but they went back to the owners with sticky labels describing the problem items.

@Hubertszcz you might also consider dropping your sample rate to 32, 16 or even 8 kHz. Do you actually have target species calling at frequencies over 16 kHz. Less data volume means fewer writes to the card. Also bear in mind that short audio bursts have storage and processing overheads compared with fewer longer bursts.

Is there an eco-battery? Well remember that half of the power you pump into a NiMH battery is lost as heat during charging. With correct charging, most types of rechargeable lithium batteries are only losing around 8 to 12 % as heat. Also with Lithium I don't think it is the mining as such that has to be destructive, rather the bad practice and corruption around some sources. A bigger concern is some components such as cobalt and nickel in those cells. LiFePO4 cells do not have the same concerns but they work at a lower voltage and I don't think you will find them in a size to fit an audioMoth case. Happy to be wrong about that though.

That's really interesting. Never considered the type of microSD card having such a noticeable effect on power consumption.

<1 mA certainly sounds like a breakthrough for this kind of device. I hope you are able to report back  with some real world performance information about your project @jcturn3 . Sounds very promising. Will the device run directly off the optional solar cell or will you include a capacitor since you cannot recharge the lithium thionyl chloride cell. I had trouble obtaining the Tadarian TL-5920 cells in Australia (they would send me old SL-2770s though) so I took a gamble on a couple of brands of Chinese cells (EVE and FANSO) which seemed to perform the same job without a hitch. Maybe in the USA you can get Israeli cells more easily than Chinese ones? 

Message me if you think some feeding sounds, snoring, grooming and heart sounds of koalas would be any use for your model training.

Really interesting project. Interesting chip set you found. With up to around 2mb sram that’s quite a high memory for a  ultra low power soc I think.

It might also be interesting while doing your research thinking about if there are any other requirements people could have for such a platform with a view towards more mass usage later. Thanks for sharing.

I remember the study in EA when they painted cows with zebra strips to stop the Tsetse fly bites. Sometimes it is the simplest things that work