time_t addMinutes(time_t t, unsigned long minutes) {
return t + minutes*60;
}
nextBatteryReadingTime = addMinutes(n,1);

It is defining a function called addMinutes() that returns a value of type time_t.

I have no idea what sort of value that is. It must be defined elsewhere in the code that you did not show us.

The function needs two parameters. It calls one of them t and it has also the type time_t. The other parameter is called minutes and its type is unsigned long.

It takes those parameter values, multiplies the minutes by 60 and adds it to the t value and it returns the result.

I suspect you will be able to figure out the last line yourself.

time_t getCurrentTime() {
** // returns number of seconds since 1970**
** setClockPower(HIGH);**
** setSyncProvider(RTC.get); // the function to get the time from the RTC**
** time_t n = now();**
** return n;**