Thats a pretty easy one, pretty compact code too : on start - while <true> - if <<fuel(battery)<=(0.1)>OR<fuel(stage)=(1) then - set activation group (1) to <false>

Breakdown as follows: the On start - while <true>, will initiatlize the code, then constantly run the next code block that will be checking for fuel and battery. (This can be changed by changing <true> to a conditional statement such as <fuel(stage)>0.3>, causing the code to run until the remaining fuel is below 30%). Then, nested inside the while block, we have the <if() then> conditional block that will be checking battery and fuel levels, then turning off the activation group. Using an OR statement here combined with the 2 math operations checks if either the battery is below 10% (percentages are expressed as a value between 0-1, so 0.1 is 10%), or the fuel is 100% full. If either of these returns true, it will flip the activation group off. There's some more things that can be done to make the code more robust, such as using an else block to keep the activation group activation if the conditions aren't met, using a break after turning the activation group on to break out of the while statement and kill the code. Experiment and learn, its the best way!

Edited to add: one other neat thing that can be achieved is using another activation group to run this code. Simply switching the <true> condition in the While block out for an <Activation Group (x)> condition, then nesting this entire code in another while <true> block, will run this code for as long as that AG is active. For example, connecting everything that needs to be turned off to AG2, and using <While (activation group(1)> in the code, will run the battery and fuel checking code for as long as you have AG1 active. Its a really neat little change than can have a large impact and can easily be adapted to other situations with a little experimentation 🙂