Ant bot only last 58 seconds before stopping. Have a Lipo .6A 7.4V

Hi!

I require your help regarding a problem I’m encountering.

I am new to robot building and just completed my first antweight bot (Fingertech Viper). I put it in a test box to safely test the weapon and it only ran for 58 seconds before the weapon and the motors stopped working. I got out the charger (B6 Pro X Charger) and set it to .6A 7.4V (2S) as it indicates in the manual. It read on the charger screen that the battery still had 6.3V left on it. I charged it back up to 7.4V and put it back in the box with the same result. It ran for just under a minute and died. When I hooked it back up to the charger it read 6.2 V. What am I doing wrong? Why would it not keep running when it has over 6V left on it?

Thank you so much in advance for your help!

What battery are you running volts and capacity?

120mAh
180mAh
250mAh
300mAh
360mAh
450mAh
850mAh
1000mAh

It is 300mAh

I’m not sure what’s going on because they claim that running 2 9V batteries yields a 2 hour run time…

https://www.fingertechrobotics.com/proddetail.php?prod=pc1604