Using a battery not specifically confirmed by the manufacturer for your device can be risky. While the RC30-0248 battery may physically fit in both the 2019 and 2020 Razer Blade 15 Advanced laptops, there can be differences in voltage, capacity, and compatibility that are not immediately apparent. It's best to contact Razer's official support or check with Razer user forums to see if others have successfully used the RC30-0248 battery from iFixit in the 2019 model. It's essential to ensure compatibility to avoid potential damage or safety issues.