Battery advice and discussion, Li-SOCl2

[Torje]

Hello Nordic and Community!

We are considering to use Li-SOCl2 batteries for our nRF9160 device. These have a good voltage and extremely low self-discharge, which makes them a great alternative to Li-Po (when non-rechargeable is viable).

The downside, as I have understood, is that they are not as good with peak currents. Our product is a "pure nRF9160"-device, with only GNSS+LTE-M. No external sensors or actuators.

We are considering using 2xAA batteries from Saft. These have 250mA pulse capacity. The "extreme peak" in nRF9160 data sheet is 435uA . So, with two in parallel we should be good. But I'm worried it might not be enough when batteries are more than 50% drained. Sudden peaks might kill the device, effectively decreasing the life time by a lot. Alternatives to work around this is to use big capacitors with the batteries, or maybe use 3xAA. We do not want to use LSH-batteries as they only come in bigger packages.

My question is, should I be worried about peaks or am I "well inside" the worry-area with 2xAA? Does anyone have any experience with Li-SOCl2 with the nRF9160 to share? Do I need batteries with caps, like in the picture? 

Thank you all for all and any help!

Kind regards,

Torje

[Kenneth]

Hello,

I don't think we have any direct experience with this, but I could find some cases that mention Li-SOCI2 (see links below in case they can provide some more information, at least I can't find anyone mention any failures). In general, Li-SOCI2 - 3.6V nominal voltage should work, but not so good performance over temp and maybe you would need a DD size to support LTE operation. But although large, this should be a possible option.

Possibly relevant cases I can see mention the battery in question:

https://devzone.nordicsemi.com/f/nordic-q-a/70455/optimal-way-of-putting-nrf9160-into-low-power-mode-without-shutting-down-the-power 
https://devzone.nordicsemi.com/f/nordic-q-a/69996/nrf9160-tx-current-duty-cycle-configurable 
https://devzone.nordicsemi.com/f/nordic-q-a/66557/nrf9160-current-consumption-continuous-and-peak-during-network-discovery   

Hope it helps,
Kenneth

[Torje]

Thank for your reply, Kenneth, and for the resources. 

After my own research, it seems Li-SOCl2 have better performance in low temp than Li-Po/Li-ion. I can't really see any better alternatives than Li-SOCl2. The rechargeable ones have too high self discharge, so long lifetime doesn't seem realistic at all. Our device, with 5+ years of battery, doesn't need to be rechargeable. Before they are empty, we'll have new products out anyway.
The Li-SOCl2 often come with different specs; either high capacity or higher peak current. I've found AA-batteries with 2Ah cap, 400mA continuous and 800mA peak, 1% self discharge per year (these are the "high peak"-type). A couple of these bad boys in parallel would give me a lot longer life time than the 5000mAh Li-Po I was considering at first, and I should be well within the specs even at cold temp. (A 1S2P-pack of these with connector is 1/2-1/3 the price of the LiPo as well.)
I prefer the AA-size to the D, as they won't build too much in height. I have space left and right, but not upwards. 

But there's always the uncertainty. Choosing the right battery is no simple task. Do you (or any other community member) have any thought about this? What batteries are generally considered viable for long-term operations? (If I chose 1.5V batteries, I would need like 6 to get the right voltage and cap from the ones I've found - and this costs too much space).

It seems to me the Li-SOCl2 are heaven sent, so there might be something I'm missing.

[charleshaf]

Would love to hear how this went!

I thought NRf9160 needed at a minimum 3.2V so even 2x1.5V batteries wouldn't be enough.