# Simplest way to measure 4 cell LiPo battery State-of-Charge during discharging

For testing purposes, I need to know an aproximate percentage of the battery charge in order to know when the battery must be recharged. It doesn't need to be accurate at all, p.e. a simple signal (LED) which warns you about low battery level. Easy to implement since I cannot spend much time on this now (after testing I will go for the fancy option), so I guess fuel gauges (unless there is an evaluation board ready to use) are not considered by now.

I'm using a standard charger and I have all this information during charging, therefore I only need a solution during discharging.

• All you can do is pick a voltage at which you think you have reached your warning level and light your LED when you reach it. Take a look at this question for hints How does voltage progress during discharge of a battery? Commented Jan 25, 2018 at 12:16
• What is the Ah capacity and maximum continuous discharge current rating of your battery, and what is the minimum and maximum operating current of the device? Commented Jan 25, 2018 at 15:34
• this are the specs--- Minimum Capacity: 20000mAh -- Configuration: 4S1P / 14.8V / 4Cell -- Constant Discharge: 10C -- Peak Discharge (10sec): 20C Commented Jan 25, 2018 at 18:43

With a simple voltage treshold you'll need to know and stick to a specific discharge rate. Otherwise this method will be useless. LiPO discharge is typically with a sharp knee before voltage drops fast. You'll need to prevent getting that far. But depending on the discharge rate (expressed in C, e.g. for 1000mAh 1C means 1A) the graph shifts up and down.

On the other hand, TI has many BQ devices that are gas gauges and they do provide development boards.

I just found this option: Protection Circuit Module (PCB) for 14.8V Li-Ion Battery Pack (4A limit) with Fuel Gauge Socket

Together with: Fuel Gauge for PCB of 14.8v Li-Ion Battery Pack

Since the connection diagram shown in the figure bellow implies using the balance connector, and that one is used as well for the charger, the only option is connecting and disconnecting this socket manually...

The PCM has the charger function as well, but I still don't know what input voltage tolerates to be charged.

• It's not clear whether you have posted this as an answer to your question or an expansion of the question. The first is OK but the second isn't because the information then belongs in the question. Commented Jan 25, 2018 at 19:05