72v battery showing 3.2v with voltmeter

[thomasrtg]

Hi everyone,

I have tried to google my issue but I haven't found anything relevant.

I have a 72V lithium ion battery (with BMS) on a custom build ebike, I was riding it this afternoon and at some point the motor stopped spining for no apparent reasons (the battery was arround 30-40% not sure of the exact voltage or percentage). I have checked all the connections and everything seemed to find. Then I have decided to measure its voltage, and instead of showing a 60~70V I had this weird 3.2 V showing up. I thought it was the bms that had turned of the battery for low voltage protection so I put in charge. After few hours, the battery was still "off" and the controller or battery gauge wouldn't boot.

There is no on/off switch on this battery pack, there is only one for the ESC.

I am not an expert with batteries as you can imagine , do you guys have any suggestion on the issue it might be ?

thanks in advance.

 

[Hwy89]

Make sure your meter is working properly and not in need of a fresh battery. Measure the output of the battery right at the terminals. If there is still no voltage open the case and measure right from the positive and negative ends of the cells. When you open the case you might find a fuse.

 

[thomasrtg]

Many thanks for your reply, I have some news here.
I have unplugged the battery of everything (esc and voltmeter gauge). While unplugged I have waited few seconds and tried to measure the battery again. The voltage is now 67V so I guess the bms was doing its job and protecting the battery of something.

I then have plugged back the battery to the controller and also the voltmeter to check the voltage under load.
When the battery is under load, the voltage drops to 57V and then cutt off. 56V being the low voltage cutt off announced by the manufacturer, I guess the bms is just doing its job and turn off the battery.

My question now is: what is an acceptable voltage drop underload of a brand new battery (supposed brand new) ?