If you have 12V outlets, you can use an appropriate automotive Power Adapter. Here are some examples currently marketed by Apple:
- mophie USB-C 20W Car Charger
https://store.apple.com/xc/product/HQ442ZM/A
- mophie Dual (USB-C/USB-A) 32W PD Car Charger
https://store.apple.com/xc/product/HQ452ZM/A
- mophie Dual USB-C 40W PD Car Charger
https://store.apple.com/xc/product/HQ462ZM/A
Most models of iPad require a Power Adapter rated at 12W (i.e., 2.4A @5V) or greater to reliably charge. Recent models of iPad optimally charge from a 20W USB-C Power Adapter.
Many in-vehicle USB ports, such as those associated with vehicle infotainment systems, cannot source sufficient power to charge an iPad. Unless explicitly designed for charging high-power devices, these ports are typically limited to 0.5-1A @5V (i.e., 2.5-5.0W).