[k_semler]

If you are doing it over an activesync via USB connection, it doesn't really matter. The reason why it is recommended that you have a 50% charge or higher is because if you are doing it the memory card route with no external charger/USB connection, your battery could die before the new ROM gets flashed. Failure to complete a ROM flash will most likely brick your phone. The reason it is reccomended to have a 50% charge or higher is simply risk management.