All of the first-page results do just dumb nominal capacity divided by current calculation, which is pretty useless. This Microchip one seems bit more clever, but it is limited to Microchip microcontrollers only and is a separate installable application, so that is no good either: https://www.microchip.com/SWLibraryWeb/product.aspx?product=...
One of my unrealized project ideas was to create a battery life estimation calculator, something you could feed in battery configuration, some power supply details (efficiency, cutoff), and consumption figures and get an estimate of battery life. The log-log charts are not all that easy to read and have only limited number of curves available.