By "the best way", do you mean easiest, or cheapest?
For me, the "best" way is to buy an auto/air DC adaptor. I have used an inexpensive AC inverter to power and recharge the laptop, but it is not the best way. The inverter creates interference on my 2 meter ham radio that is unacceptable. The other problem is all the cords and cables and power blocks, not to mention the power losses in the conversions from DC to AC and back to DC.
To mention a few: Inverter cable->power cord->transformer block->power cord->laptop. GPS power cord -> GPS -> laptop (for navigation or APRS). External GPS antenna -> GPS. Handheld ham radio power cord (12V) -> Ham Radio (for APRS) -> computer cable. Ham Radio antenna cable -> Ham Radio. :Wow1:
So you see that while this may not be your setup, reducing the number of cords and cables and coversions is an advantage.
The adaptors sell for around $100 online. You can pay less if you look around. I just ordered the adaptor today and paid $98 shipped.