Charging battery while having voltage sensor across it

Is it safe to have a voltage sensor hooked up to a battery (and feeding measurements to an Arduino) while the battery is being charged up? If so, are there any downsides to this? (e.g. not charging as effectively since some little current is going through the voltage sensor)

The battery charging method is relatively slow (using photovoltaics).

No, probably not (no downsides).

What kind of battery ? What currents and leak currents are involved ? What is your sensing circuit ? Which Arduino board ?

Suppose you have a 12V battery and a charge current of 2A and an Arduino Uno and analogReference(INTERNAL), and a voltage divider with 10k to ground and 150k to the battery. The current by the 150k will be 72uA. That is less than 0.00004%.

I can't see any issues, just bear in mind that the battery voltage may get a lot higher than you have allowed for with your voltage divider, it depends on battery type but a 12V lead acid would get to about 15V at full charge.


A good charger won't let a lead-acid battery voltage rise above 14.4V - this causes excessive electrolysis and heat-generation! But you would want your voltage divider to be able to measure at least this high.

Use sensible values in a voltage divider (as high as you can get away with without compromising accuracy of the ADC - for the Arduino that usually means using about 10k as the lower arm of the divider - this means only 0.5mA is being "wasted" in the divider.)

I work with 24V solar systems a lot and with a three-stage charger the absorption voltage is around 30V, that's for AGMs though, other chemistries will be different I assume.


Thanks for the information.

In my application, the Photovoltaic won't charge the batteries to full. Its purpose is just to try and extend the battery life (since the batteries will be powering measurement devices at a remote location). The voltage divider I'm using is 1k from Vout to ground, with 15.7k total from measured voltage to ground. (ratio of 1/15.7)