were that true the charge time would be longer than the run time (not strictly true, if the load is bursty what you say could conceivably be true) its somewhat

were that true the charge time would be longer than the run time (not strictly true, if the load is bursty what you say could conceivably be true) its somewhat difficult and fussy to do power management in the way you would expect - that the input power is used to power the computer, and whatever is 'left over' is used to charge the battery. this is just skimping on engineering bandwidth and a few extra components