That's exactly how my Solar System worked if I had my inverter turned on in the day.
If load is less than charge. It keeps charging.
If the load is greater than the charge it goes flat, but slower than it would with no charge.
It all comes down to amps in vs amps out. and sometimes total amp hours if you need some "buffer" room for start up peaks....
That assumes your charge controller doesn't have a fit for whatever reason like detecting an excess drain and deciding it's a fault...
Many charge controllers will have a hissy fit wen they notice the battery is going flat as they put charge in. Really cheap (and sometimes nasty) ones seem to have less safety features and will do this less. If the battery keeps charging. You can normally "Trick" the controller into thinking it's plugged into a really big battery when it's actually much smaller. If you turn the load on and off a lot. Almost all chargers will decide the battery is stuffed eventually.
If you want to give some more info. Like Size of battery, charger type and power, and a bit about the load we can help you find a solution better..
