I just kept pressing "Unseal / Boot" and it finally unsealed. Any ideas why it doesn't work most of the time ?

Because MSP430 was not isolated from SMBUS. It serves as main master, nlba1 serves as secondary master, bq30z55 serves as a slave. So in the multimaster environment there is big probability of interference and packet collision because both masters talk with a slave at the same time. 

@djibattworkshop thanks you ! Makes sense. Is there a work around ? Should I just keep trying to unseal until it works. 

Which hardware was used to work with a battery, ev2300, ev2400 or Nlba1?

Was battery switched ON or OFF by push-button before Unseal?

Does any LED blink while Unseal try ? 

@djibattworkshop thanks for the reply. I am using the EV2400. I don’t think any LEDS came on when trying to unseal. It was locked out from power on. I might have tried to turn it on to see if that would help unseal it but it didn’t. 

@macjax 

Repeat the unsealing many times until the software finds a free slot on the bus.

Posted by: @macjax

I don’t think any LEDS came on when trying to unseal. It was locked out from power on

 Dji Mavic Pro batteries based on msp430 mcu, and it allows to press Power On button and to switch On the LEDs even in the Locked state. Not to be confused with Dji Mavic Pro 2 battery where chip is different and does not allow to check LEDs when Locked. 

Posted by: @macjax

I might have tried to turn it on to see if that would help unseal

 It is poor practice. Switching the battery On by push button will activate msp430 which serves as main smbus master and could cause conflicts on the bus and interfere unsealing. 

 Battery should be Off by push-button before unseal. No LEDs should be lit. 

@djibattworkshop yes. That’s how I initially had it and only turned it on because it wouldn’t unseal. Good to know this info though. I have another battery that I’m going to try and see what happens. Thank you for the reply. 

If you got issues with unsealing, measure the voltages on SCL, SDA pins relating to GND and post a values.