How to monitor the remaining energy in a Lithium based battery

[cagriuysal]

Hello,

I am working on wireles sensor networks topic and I need to monitor the battery level of my sensor nodes in the network. However, as far as I know, lithium based batteries have a flat voltage over time curve, so it is not possible to simply measure the voltage of the battery output. Am I correct?

My sensor nodes are low capacity ones and they dont (and most probably they cannot) have any hardware mechanism attached to them to monitor the battery. What I need to know is to detect whether the battery level of a node is in a critical situation or not. Is it possible to do it without adding any additional hardware?

Regards,

Cagri

 

[IRstuff]

No battery has a perfectly flat profile with a perfectly sharp cutoff. You just have to pick a spot, and take the lumps for replacing batteries that might still be quite full.

Lithium batteries nominally have 3V at the start. According to Duracell's Li battery bulletin, they are essentially completely discharged at a 2V output, so 2.5V might be a good stopping point. According to the curves in the bulletin, 2.5V would put you at about 90% of capacity.

TTFN

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[cagriuysal]

Thanks for the response, I will consider that.