Does anyone know how often Android refreshes battery statistics? This screen is
Settings > Battery. This may only apply to Android versions >4.0.
I believe it is real-time. Meaning, the stats are always updated as the battery is being drained (or charged).
You can check the source code of battery history and battery history part of Settings. I hadn't got time to properly check it out, but from an initial scan, I think it's updated every time the app is started. The file from which the app generates the statistic however, batterystats.bin, is probably collected at real time as the system starts and kills apps and system services are turned on and off.