Short answer: yes. The DR-FZ100 takes USB input, so a 12V socket adapter with a USB output can top up two NP-FZ100 packs while you drive — roughly 4 to 6 hours for both, or 3 to 4 hours with a PD-capable adapter. The question is not whether it can be done, but which adapter you use, how the case copes with the voltage dip when the engine cranks, and how hot the cabin gets in summer. What follows covers the power path, adapter choice and a charging rhythm for the road.
How the power chain works in the car
The chain runs: 12V socket, adapter stepping down to 5V (or negotiating a higher PD voltage), USB cable, charging case, battery. If any link is weak, the symptom is always the same — slow charging or no charging at all.
The second link is the one people overlook. A cheap adapter rated at 2.4A can drop below 1A when the supply voltage sags; the case keeps charging but crawls. That is not the case’s fault, and a different adapter fixes it.
Choosing a car adapter
Three criteria, in order of importance: output stable at 2A or above, independent over-voltage and over-current protection, and PD output support. The first two decide whether charging is reliable; the third decides how fast it is.
| Adapter type | Typical output | Two packs, full | Where it fits |
|---|---|---|---|
| Old single-port adapter | 5V/1A | About 6-8 hours | Not recommended, emergencies only |
| Dual-port adapter | 5V/2.4A per port | About 4-6 hours | Fine day to day, phones as well |
| PD adapter | 20W and up | About 3-4 hours | Long trips, multi-battery rotation |
With a dual-port adapter, watch the split: plug in a phone and the case together and each takes half the output, so the case charges noticeably slower. If you are in a hurry, run the phone from a power bank and let the adapter feed the case alone.
The voltage dip at startup
When the engine turns over, battery voltage sags briefly to around 9V before recovering. Many adapters restart at that point, and the charging case drops out and resumes with them. Once is not a problem, but a dozen restarts a day is not kind to any charging circuit.
The fix is simple: plug the adapter in after the engine is running, and unplug it before you switch off. That habit also solves a second problem — it stops the adapter drawing from the car battery during long stops.
As for whether charging with the engine off will flatten the car battery, the arithmetic settles it: two NP-FZ100 packs total around 33Wh, and with conversion losses perhaps 50Wh. Against a car battery of 45Ah or more that is a rounding error. The real risk is not these two packs but leaving the adapter plugged in and drawing idle current for days, which shows up quickly on a battery that is already tired.
A charging rhythm for long shoot days
The idea is to put charging inside time you were already spending behind the wheel, rather than hunting for a socket on arrival. A three-hour drive is enough to take two packs from empty to full.
- Charge everything at home the night before, so the car is only replacing what you used, not starting from zero.
- Plug in as soon as you get in, and put the case somewhere ventilated near the passenger footwell rather than on the dashboard under the windshield.
- Half an hour before your first location, feel the case and confirm at least one slot has gone green.
- Between setups, drop used packs straight back into the case and keep charging on the way home, so the cycle continues.
- On multi-day trips, top everything up once each evening from the hotel socket, in case one day’s drive was too short to finish the job.
The point of the routine is never to let all your packs run down at once. One full, one in the camera, one on charge is enough to carry a normal day of moderate shooting on three packs.
Summer cabin heat is the real risk
A closed car in direct sun can reach sixty degrees or more. Charging at that temperature will at best trigger thermal throttling and at worst pause altogether. Worse still, long storage at high temperature accelerates cell aging invisibly; a few months later the capacity is visibly down.
Three practical rules: keep the case off the dashboard, the rear parcel shelf and the area around the gear lever, where sun lands directly; if you park for more than half an hour, put the case in the glovebox or take it with you; and if it feels properly hot to the touch while charging, stop, let it cool, then resume.
The same applies to the packs themselves. A camera bag left in the car with spare batteries inside is a common and genuine cause of early capacity loss. Cold is the opposite problem, and the cold-weather test covers that in more detail.
Working alongside video shooting
On a long trip shooting video, packs drain far faster than they do for stills, and topping up in the car may not keep pace. When that happens, external power at fixed positions plus batteries on the move is the steadier combination; the FX3 and FX30 power setup covers the options.
For the case’s own specifications, how to read the indicator lights and day-to-day care, see the dual-slot charger section, which has the full operating notes.
FAQ
What if one 12V socket is not enough?
Use a one-to-two socket splitter, but keep the total draw inside what the car’s wiring is rated for. Most cars fuse the socket at 10A to 15A, which comfortably covers two adapters and a dash cam, but do not hang a high-power inverter off it.
Will the case work on rough roads?
Yes — once a pack is seated it will not work loose. Still, tuck the case into a seat gap or a storage bin so it does not fly out under braking. On long stretches of bad road, dust collects on the contacts, so wipe them with a dry cloth every so often.
Can I leave it charging with the adapter plugged in while I am away from the car?
Briefly, yes; for long periods, no. The car battery keeps discharging, and charging unattended in a hot cabin in summer is a risk. If you are stepping out, take the case or unplug the adapter.
The adapter says 3A, so why is charging so slow?
The rating is a theoretical peak. Real output depends on the cable, contact resistance at the plug and how stable the car’s voltage is. A short, thick cable plugged straight into the socket rather than into an extension often fixes it immediately.