Powering a node with (18650) lithium batteries

[LastSamurai]

Hi,
I am always looking for a good option to power some of my (future) sensor nodes. Yesterday I read an article where someone was using 2 parallel 18650 lithium batteries. They have more than 3V (most of the time), so they should work with the LDO of the pro mini or something like an ams1117 and they have a very high capacity. Also they are rechargeable and the price is high but still acceptable (as you wont need another one for years).
Sounds too good to be true for me and afaik you need some complex control circuits for lithium batteries. Is that right?

Are there any other nice options? (Beside coin cells which are cheap and small but with a low capacity and 2xaa which is cheap and has a better capacity but is very big. One aa sized lithium battery with a high capacity sounds nice in comparison...

[mfalkvidd]

@LastSamurai 2xaaa might be a good alternative if you think 2xaa is too big. Their performace compared to weight (and probably volume) is a bit worse, bit this might not be a problem depending on your application.

An aa-battery weighs around 23g and has a capacity of around 2,400 mAh, resulting in 104mAh per g.
An aaa-battery weighs around 11.5g and has a capacity of around 1,000 mAh, resulting in 87mAh per g.

The 18650 can be charged by a cheap circuit like http://www.ebay.com/itm/251920272050 (this is the listing I am using but you should be able to find something similar)

2 parallel 18650 will be much larger than 2xaa though. But in most cases you would probably only need one battery.

The larger coin cell batteries, for example the CR2477 at 1,000mAh might be a good alternative as well.

CR123A has quite a lot of capacity compared to their size. Example: http://www.aliexpress.com/item/Free-Shipping-1300mAh-3-7V-16340-CR123A-Rechargeable-Battery-Li-ion-Battery/32411166429.html

[LastSamurai]

@mfalkvidd Thanks you! Thats quite some information.

I wouldn't need to load the lithium batteries directly in my sensor but only drain/use them. So there is no special circuit needed for that, right?
I am currently leaning towards either the CR2477 because of its small height, or the 18650 because of the large capacity.

If someone has more useful information about batteries feel free to add them here, I think it's one of the core problems when building nice sensors.

[mfalkvidd]

@LastSamurai said:

I wouldn't need to load the lithium batteries directly in my sensor but only drain/use them. So there is no special circuit need for that, right?

Correct.

I'm not sure on how to best address the power supply problem. I would like to se a future where I have several hundred sensors. If the sensors average 2 year battery life and I have 180 sensors, I would have to switch batteries in a sensor every 4 days. That's no fun.

Energy harvesting might be an alternative. References: .
https://forum.mysensors.org/topic/1917/energy-harvester/
https://forum.mysensors.org/topic/279/energy-harvesting/

I have't found a really good solution yet but on the other hand I don't have that many sensors yet either

[LastSamurai]

@mfalkvidd Thanks!
As energy harvesting doesn't seem to be "there" quite yet I will stick with both coincells and the 18650 lithium batteries as alternatives for my project (depending of the needed energy and space constraints of the single boards).
Rechargeable or harvested power seems to be the only good solution for larger quantities of sensors in my opinion.

Does anyone of you know where to buy cheap 18650's that don't explode and don't lie too much about their capacity