Short answer: the TNP-FZ100 records normally in an A7 IV or an FX3, but “charging while shooting” will not rescue a long take — once the pack is in the bay its own Type-C port is completely covered, so any top-up runs through the body’s USB-C input, and whether that holds depends on the body and the supply wattage, not on the battery. What really caps recording time is body heat, not capacity. For two or three hours or more of continuous recording, neither swapping packs nor charging while shooting is a good trade; external power is the steadier answer. Below we separate the real limits of the three routes.
First, one thing to clear up: the port on the battery is unusable in-camera
The direct-charge port on the TNP-FZ100 sits on the side of the pack itself. Once the battery is seated in the bay, the wall covers it completely and there is no room to route a cable. So in practice “charging while shooting with a TNP-FZ100” has exactly one form: the pack powers the body as usual, while a cable runs from the camera’s USB-C port to a power bank or a PD supply.
That route only works if the body accepts USB power. The A7 IV, A7S III and FX3 all take PD over USB-C, and with a suitable supply the camera draws from the external source first, so the pack’s discharge slows markedly or stops altogether. Older bodies support USB charging but not USB power — with a cable attached they keep drawing from the battery, only more slowly. Check your camera’s manual on this point.
Three supply routes, and roughly how long each lasts
The table gives orders of magnitude for 4K at a normal bit rate, around 22°C ambient, a single camera and continuous recording. Actual time depends heavily on bit rate, frame rate, screen brightness and whether a fan is running.
| Supply route | Continuous recording | Strength | Main limit |
|---|---|---|---|
| TNP-FZ100 alone | About 1–2 hours | No cable, maximum mobility | Swaps interrupt the take, and cold weather cuts it further |
| Body USB-C to a PD supply | About 2–4 hours or more, depending on cooling | No need to stop, low cost | Tethered by the cable, heat accumulates |
| Dummy battery plus a large supply | Set by the external supply’s capacity | Genuinely continuous power | Needs extra parts and cable routing |
The third route replaces the real pack with a dummy of the same shape, wired to an external supply or a USB power module. It removes capacity from the equation entirely, which suits fixed-position interviews, livestreams and conference recording. For the wiring details, see our dummy battery power guide.
The three real limits of charging while shooting
Limit one: is there enough power?
A recording body draws in the 5–10W range, and more at high bit rates, with stabilisation on and the screen bright. Feed it from an ordinary 5V/2A power bank and the input may only just match consumption or fall slightly short, so the pack keeps draining — you have moved from one hour to two, not to unlimited. A PD supply of 18W or more is what gives the charge a chance to actually hold.
Limit two: heat adds up
Charging produces heat and recording produces heat; do both at once and the interior warms faster than with either task alone. The A7 IV is fairly sensitive to temperature during long 4K takes, and recording while plugged in brings the overheat warning forward. The FX3 has an active fan and more headroom, but a blocked intake or a hot environment will still trigger protection.
Limit three: a cable changes how you shoot
Plugged in means the camera cannot move freely; handheld follow shots, gimbal work and quick repositioning all suffer. Many people conclude that carrying two more packs and rotating is preferable to living with a cable — which is the argument for a dual-slot case.
When to give up on charging while shooting
The test is simple. If a single take runs longer than the pack can supply and you cannot stop in between, do not count on charging while shooting — go to external power. Interviews, lecture capture, livestreams and multi-camera stage work all fall into that group.
Conversely, for documentary following, weddings and moving exterior work, the cable costs more than it gives. The right approach is three or four packs, all charged overnight in a dual-slot case, swapped between segments during the day. In that workflow the direct-charge port on the TNP-FZ100 earns its place: at lunch, any USB outlet will put half a charge back into the pack you have just pulled.
Video power on the FX3 and FX30 involves finer trade-offs. Our FX3 and FX30 video power guide compares the two bodies, including cooling design and recommended supply wattage.
A configuration that rarely goes wrong
- Fixed main camera: dummy battery on a large external supply, with the pack as a buffer for power interruptions.
- Moving work: TNP-FZ100 in the body, two spares in the bag, everything recharged at the end of the day.
- Mixed situations: body USB-C on an 18W-plus PD bank, as an extender rather than a substitute for capacity.
- Summer outdoors: keep the body out of direct sun, let it cool between takes, and never leave a plugged-in camera sealed in a bag.
What these have in common is that runtime is never bet on a single method. The battery buys mobility, the cable buys duration, and each covers its own stretch. More accessory combinations are listed in the TNP-FZ100 catalogue.
FAQ
Will the FX3 overheat recording 4K from a power bank?
It can, but it is more forgiving than a fanless body. The FX3 has active cooling and typically runs a long time at room temperature, provided the intake is not covered by a hand or a sticker. In direct summer sun, every body loses headroom.
Does charging while shooting cause swelling?
Not in normal use. Swelling is mostly tied to prolonged heat, failed overcharge protection or cell quality. Keeping the camera out of a sun-baked car and avoiding unknown chargers are the more effective precautions.
Will an ordinary power bank extend recording time on the A7 IV?
It will extend it, but by how much depends on the bank’s output. A 5V/2A output mostly just slows the decline; holding the level needs a PD fast-charge tier. Confirming that your bank supports PD output before you leave saves more weight than an extra battery.
Does swapping the battery mid-take lose the clip?
It ends the current clip. To change packs without stopping, you need external power to carry the camera, or a supply design that supports two batteries. That is why fixed-position work leans toward a dummy battery.