Skip to content

Battery Voltage versus Time

Jump to bottom
Rob Jones edited this page Sep 29, 2016 · 9 revisions

Here is a plot of battery voltage over time for 2500mAh LiPoly battery attached via PowerBoost 1000C to a Raspberry Pi Zero.

Voltage graph full cycle

At the start the battery is fully charged and the PowerBoost has a USB power supply attached. The voltage is around 4.15V

At around 5 minutes, the USB power cord is removed. The voltage drops immediately to around 4.025V. I do not know why this happens.

The voltage then decreases slowly until around 70 minutes. The rate of decrease is not linear but is close enough that you can predict the remaining battery life from the voltage well enough. There are fluctuations in the voltage. I do not know the cause of this.

In principle a LiPoly battery voltage should vary from 4.2V fully charged down to 3.7V when it is drained. For the purposes of the pi_power project I treat 4.05V as fully charged and 3.75 as drained. This gives a voltage range of 0.3V.

At 70 minutes, the USB power cable is reconnected and the PowerBoost starts to recharge the battery. The voltage jumps up almost immediately to around 4.1V - but this does not mean that the battery is again fully charged. Charging continues slowly for the next 2.5 hours with the measured voltage slowly increasing. The PowerBoost has a yellow LED that indicates charging. This eventually turns green to indicate that the battery is fully charged.

Clone this wiki locally