Yes, you can. However, I would suggest to you that it would probably be easier to implement in Stateflow if you are planning to do simulation of events. Or perhaps combining Stateflow with Simulink.
If it is important to monitor the current battery levels while charging and discharging, then a Simulink component could be useful. But if it is acceptable to just say, "Okay, here's a recharge event, new charge is given by this formula" and on the timescale the event is then "over", then Stateflow would be more appropriate.
