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For my wild life camera, I want a small cell that can provide 0.5W for 8 hours or more. It doesn't seems rechargeable lithium ion batteries have that energy density. I don't mind if the cell is non-rechargeable, so I've considered the lithium coin cells and zinc-air batteries.

But it seems the internal resistance on those are terrible: For a CR2477, I estimate the resistance at 910 ohms! Energy density = 2.96 MJ/L

For a 675 hearing aid cell, I estimate 34.7 ohms. Energy density = 6 MJ/L !

So if I use those, there's no way I can draw 0.5W, if at all, without having all the energy consumed by IR? (is IR the only factor causing lower capacity?)

Is this a fundamental limitation to those battery chemistries or can someone point me to cells that allow higher current draw?

According to Wikipedia's energy density page, it claims there are non-rechargeable lithium batteries with an energy density of 4.32 MJ/L. That would be awesome, but where do I find them? (I'm only seeing 2.96 MJ/L for a CR2477 coin cell).

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    \$\begingroup\$ What's the problem with internal resistance? keep it cool, and don't draw much current from it.. invest in a super-capacitor to buffer between the coin cell and the output. \$\endgroup\$ – KyranF Oct 31 '14 at 10:29
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    \$\begingroup\$ 0.5W at 3V from a coin cell is 160mA, which is not too bad if the load is not for a long time, you can easily buffer than with a capacitor. But of course, the space taken up by the cap probably outweighs getting a better battery by far \$\endgroup\$ – KyranF Oct 31 '14 at 10:31
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    \$\begingroup\$ Good point about using a capacitor. My camera is motion activated so in theory I can power down when no motion has been sensed for a long time. But even if I do it, I think the average power draw will be > 16ma, which I think is already beyond a coin cell's short circuit current. \$\endgroup\$ – Yale Zhang Oct 31 '14 at 10:48
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    \$\begingroup\$ wow, that's a pretty hectic camera. perhaps you can find a better, low power camera more suited to this kind of sleep-wake-take-sleep action? \$\endgroup\$ – KyranF Oct 31 '14 at 10:53
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    \$\begingroup\$ I forgot to say, my camera board is only 2" x 1", so an 18650 would be too long. \$\endgroup\$ – Yale Zhang Oct 31 '14 at 12:07
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Tadiran Batteries have LiSOCl with an integrated super capacitors. Those are not rechargeable and are quite expansive compared to the more common CR types. The standard LiSOCl AA cell can manage 100mA/100mSec pulse at ~3V (Dropping from 3.6V). There are many manufacturers of such batteries (Tadiran, Saft, Xeno, EEMB and others). Of course, there are also D sized cells with 19Ah capacity and much higher pulse capabilities.

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