Here's an interesting option for field flying and charging multiple batteries, a DROK step up DC to DC converter, with voltage regulation.
This little DROK device below might be interesting, mounting it under the hood of your car permanent with a 6' charge cable and barrel connector to charge your P4 batteries and RC. Imagine just opening your hood and pulling out a cable with the charge connector on it, ready to use anytime, even with the car motor off. You could potentially do this with the DJI car charger too for $60, but this DROK unit is only $22, and more powerful. Some testing would be needed to make sure this has a "clean enough" 17.2V DC output, but I expect it would be OK. Even the DJI car charger has a little ripple to its output.
Many pilots would like to charge batteries with their car motors turned off, usually while parked in the parking lot. Most car batteries can easily handle charging 3 or 4 batteries without running the motor to recharge, assuming your battery isn't anemic and ready die for other reasons. But even then, you can't just plug a DJI car charger into the cigarette lighter and charge while parked, without the motor running. Most newer cars won't allow that (like in the 70's), the motor must be running for the cigarette lighter to work. So.... the most common alternative is to get one of these adapter cables below that allow you to clip directly to the battery, under the hood. This is perfectly doable, it's just a little more hassle with all the cables associated with under the hood post clips, running into the car or onto the ground, etc.
These adapter cables can come in handy for other reasons, but especially handy charging batteries with the car motor off, using the DJI DC charger while traveling with rental cars. But if the DROK module was permanently mounted under the hood, that would be a cleaner way to support charging P4 and RC batteries when traveling with your own car. The best part is using the 3X charger tray from DJI. You can install up to 3 batteries and walk away while they sequentially charge.
This little DROK device below might be interesting, mounting it under the hood of your car permanent with a 6' charge cable and barrel connector to charge your P4 batteries and RC. Imagine just opening your hood and pulling out a cable with the charge connector on it, ready to use anytime, even with the car motor off. You could potentially do this with the DJI car charger too for $60, but this DROK unit is only $22, and more powerful. Some testing would be needed to make sure this has a "clean enough" 17.2V DC output, but I expect it would be OK. Even the DJI car charger has a little ripple to its output.
Many pilots would like to charge batteries with their car motors turned off, usually while parked in the parking lot. Most car batteries can easily handle charging 3 or 4 batteries without running the motor to recharge, assuming your battery isn't anemic and ready die for other reasons. But even then, you can't just plug a DJI car charger into the cigarette lighter and charge while parked, without the motor running. Most newer cars won't allow that (like in the 70's), the motor must be running for the cigarette lighter to work. So.... the most common alternative is to get one of these adapter cables below that allow you to clip directly to the battery, under the hood. This is perfectly doable, it's just a little more hassle with all the cables associated with under the hood post clips, running into the car or onto the ground, etc.
These adapter cables can come in handy for other reasons, but especially handy charging batteries with the car motor off, using the DJI DC charger while traveling with rental cars. But if the DROK module was permanently mounted under the hood, that would be a cleaner way to support charging P4 and RC batteries when traveling with your own car. The best part is using the 3X charger tray from DJI. You can install up to 3 batteries and walk away while they sequentially charge.