Without the Power Converters Mod, you would have to build a RailCraft Steam Turbine. The ~210 mb Steam/t that a stack of Steam Boilers with 240 mirrors generates would only run it at about 65% though. Alternatively, you can run ~5 Industrial Steam Engines to generate 40 MJ/t of of that instead..
Run lead wire from your Factorization Steam Turbine to the Battery Box, it will charge up and to my knowledge only discharge when there is no other source of Charge and a machine is requesting power (Factorization Grinder / etc). There are visual indicators on the block itself to show how charged it is, you can also use a Charge Meter and right click on it. Additionally, when in your inventory the Battery Box retains its stored power (for the purposes of certain recipes)
Hey Raisu how can you have that much power to run with 65%?
the highste i get with the setup from above is around 44%
can you make me please a screenshot from your setup?
Edit: i get 87eu/t on the steam turbin