How to know if Battery is almost empty?

Hi guys,

I’m not too familiar with electronics and was wondering how to know if my batteries are almost empty. My Voltometer indicates a max load of 20V. When running the motor Voltage starts going down.

  1. At which indicated voltage should I stop using the motor?

  2. Is there a a tutorial out there how I can add a battery load indicator to my build?


Hello Phil
Never go below 3.2 volts per cell because the battery will be damaged, so that the batteries last a long time, I read that it was not necessary to go below 3.6 / 3.7 volts per cell!

A cheap and simple solution is to connect a Battery voltage indicator that starts to buzz if the voltage of a cell drops below a adjustable limmit i.e. 3.2v:,searchweb201602_4_10152_10151_10065_10344_10068_10342_10343_10340_10341_10696_10084_10083_10618_5725020_10307_10134_5724920_5724120_5724020_10059_100031_5724320_10103_10624_10623_10622_10621_10620_5724220,searchweb201603_51,ppcSwitch_5&algo_expid=96f07b93-0d46-47dd-90fd-f0f838d42603-0&algo_pvid=96f07b93-0d46-47dd-90fd-f0f838d42603&transAbTest=ae803_1&priceBeautifyAB=0

Thanx Guys,

that was helpful.

I’m also planning to make my own remote. How can I get the “Battery Voltage Indicator” to send a signal to the remote to activate a red LED to visualize the low voltage alarm?

You will probably use two arduinos, one in the remote and one on the ESC side. Both are linked by radio modules, e.g. standard cheap 315 MHz transceivers, or NRF24L01 which use 2.4 GHz. You will need to send the throttle signal from the remote to the ESC side via the radio modules. Those modules are often bi-directional, so nothing keeps you from sending voltage values back to the remote - or just a message that indicates low battery.

Phil, I’m relatively new to the world of batteries as well. I found this tutorial extremely helpful. It’s a little long but really covers all the bases - including your question - in detail.

Thanx Sunrise305, interesting insight into understanding LiPos

Thx Benjo,

I’m not too familiar with electronics so your suggestion is a little bit too advanced for me. Does anyone know of a tutorial video that explains how this could be achieved preferably with plug and play components I can order online.

Hey @Phil,

it is really just the same as sending the throttle values to the ESC, just the other way around. If you don’t know how to do this it could be hard for you to build a custom remote anyway, maybe you should try to build up some general Arduino knowledge by playing around with various smaller toy projects?
I am afraid there is no plug and play solution to what you want to achieve.

Those battery monitors sat_be mentioned above are now also available from Amazon. $6 for two with fast shipping.