Can a fuel gauge be dependably used between a charger circuit (which will independently regulate the charging voltage, current or both) and a battery?

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    \$\begingroup\$ What type of fuel gauge? The less accurate ones that read the voltage only or the more accurate ones having a shunt resistor to read charge and discharge currents as well? \$\endgroup\$ Sep 28, 2022 at 13:21
  • \$\begingroup\$ This fuel gauge reads voltage and current and is always connected. I posted here because, in one case, the fuel gauge reported about 50% while reporting the voltage of the battery was very near it's top off voltage value and zero current (indicating the smart charger had stopped charging). It occurred to me that the smart charger and fuel gauge could be working against each other. So posted the above question. \$\endgroup\$
    – st2000
    Sep 28, 2022 at 14:03
  • \$\begingroup\$ Something as this could be used theiotprojects.com/…,*%2026V%20%3D%2083W%20of%20power. Just use a ESP8266 and you will get your measurements via WiFi ... hackster.io/suhaspn007/wi-fi-multi-meter-7ab150 \$\endgroup\$
    – Antonio51
    Sep 28, 2022 at 15:05

1 Answer 1


It depends on the type of your fuel gauge. Most cheaper ones simply measure the voltage, and this is problematic, because:

  • the battery voltage rises when the charger is connected
  • the battery voltage drops when a load is connected
  • if you disconnect the charger, the battery voltage will slowly start dropping on ita own
  • similarly, if you disconnect a load, the voltage can slowly rise

If the gauge is connected to the battery all the time or most of the time, then what it displays may be unreliable. On the other hand, if you connect it only while charging, it has the potential to work well.

If your gauge is a coulomb counter type (the one that measures the current going into the battery and multiplies (integrates) it with the time), then it's going to work well even if you leave it permanently attached to the battery and connect chargers and loads. Of course, there will be an error, but it is much less confusing than a voltmeter.

P. S. the charger type doesn't make much difference here, as long as you pay attention to the charging current and end voltage.


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