lcalamar toggling mobile data can be done with the Quick Setting tiles or SETTINGS>NETWORK AND INTERNET>YOUR SIM>MOBILE DATA.
As for the battery usage, what network type setting are you using?
If you are on LTE Recommended/Only then your device will stick to low strength signals for LTE which obviously uses more power to maintain them.
If your carrier has a stronger 3G signal then consider switching to that.
If your carrier only has low signal strength in your area while another has better and this is a deal breaker consider switching carriers but beyond what I have mentioned there is no other practical way of mitigating this and it is certainly beyond the scope of the OS be it GrapheneOS or stock.