Battery Monitor updates all readings in the overview window once per second. There should never be a reason to increase or decrease this rate.
The curves in the history windows are being updated once per minute. If you have never used Battery Monitor on this computer, or if you have used it more than 48 hours ago, all history windows will be empty, because no history records are available for the monitored time interval. This is the intended and correct behavior.
Sometimes, you might be under the impression that values in the overview window change much slower than once per second, in particular the value for estimated remaining run time. Although Battery Monitor tries to update the readings very fast, the battery processor might not allow to be polled too often per time unit, responding with identical values for an extended period of time. Battery Monitor has no influence on this. Limitations in the battery hardware and in the operating system version you are using may cause a slower effective update rate.