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I need to monitor the charge condition of an 8V lead acid battery.

For monitoring purposes, I used a Beagle Bone Black (BBB) running Linux. It is also supplied via this battery. The battery also supplies three DC motors (switching on and off) and a camera.

Now if the charge falls below a certain percentage, the BBB should report this via SSH and shutdown.

Now my problem is:

How can I determine the state of charge? Is it sufficient to measure voltage every ~50ms and report "Low power" when the voltage is below a certain value for 1s, or do I have to use a fuel gauge IC like this one? If so, which one is easy-to-use or has a tutorial or reference project I can stick to?

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For lead acid batteries, voltage is good enough for reporting state of charge. Especially if you don't need detailed time information and just want to report "low battery".

It's not exactly linear, but it's close enough: Battery discharge curves

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  • \$\begingroup\$ Worth noting that state of charge based purely on cell voltage does not tell you the remaining capacity or health of battery. \$\endgroup\$ – John U Oct 7 '14 at 14:43
  • \$\begingroup\$ It is worth noting that different types, sizes and ages of lead acid batteries will differ, so calibrating your system to your type or individual battery will give better results. Running a full charge to half charge using a known single resistive load while monitoring will give you a good baseline. \$\endgroup\$ – KalleMP Aug 1 '15 at 9:19

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