There are two Lithium Ion battery options on the MarkSetBot/MSB.
Standard battery runs 6 to 8 hours. Big battery is 12 to 16 hours.
These numbers can be dramatically decreased if there is a lot of current (.5knts+) or if the MSB is instructed to motor itself out to the race course. The MSB is able to handle current and motoring out to the course. Both just reduce battery life.
As an example, in 1knt of current with 20knts of breeze, the 30Ah battery would likely only give you 1.5 to 2.5 hours of battery life. If you have lots of current, you should upgrade to one of the bigger batteries.
When in the MSB app, you can see battery voltage, battery % remaining, and battery Amp Hours remaining. You find that information by tapping the Battery icon in the bot menu at the bottom of the screen
You can also tell battery % remaining with a volt meter. You can determine battery life based on the following chart.
100% ==> 14.3 V
80% ==> 13.28 V
60% ==> 13.14 V
40% ==> 13.106 V
20% ==> 12.89 V
NOTE: these readings need to be done when there isn't load. So, you can't have the prop spinning when testing.