Short answer: the right way to run four packs across two cameras is not to give each body two — it is to number all four, pair them permanently by camera position, and stagger the swaps so that at any moment only one pack is recharging in the case and another is ready to go. That way you never reach a point where both bodies are flat with nothing charged. What follows is a rota you can copy directly.
The scenario: two A7S III bodies, one as the main angle (wide, head-on) and one as the second angle (side or hands), four NP-FZ100-class packs — two OEM and two third-party units such as the TNP-FZ100. Audio is recorded separately, with each take running 40–50 minutes and a 15-minute break between takes.
Step one: number and pair
Label the packs A1, A2, B1 and B2, with the sticker on the back away from the contacts and the heat path. Group A belongs to the main camera, group B to the second camera; they do not cross over or mix.
The reason for fixed pairing is that two packs used in the same body gradually converge in how they discharge, so your sense of how long a given pack will last gets sharper over time. Random allocation each day means relearning that every time. Constant mixing also levels out the wear across all four, which removes the buffer of always having one pack in better condition.
If the four are a mix of OEM and third-party, pair by capacity and condition rather than by brand. Two packs in similar shape in the same group make the swap rhythm predictable.
Step two: work out usable time per pack
| Recording format | Whole-camera draw | Runtime per pack | At 40 minutes a take |
|---|---|---|---|
| 4K 24p 10-bit | 8–9W | About 100–120 minutes | 2 takes, margin is tight |
| 4K 60p 10-bit | 9–10W | About 85–100 minutes | 2 takes, comfortable |
| 4K 120p 10-bit | 11–12W | About 70–85 minutes | 1 take, swap before the second |
The figures are ranges derived from a power model, not measurements from a particular body. Temperature, screen brightness and whether stabilization is on all shift them, and a twenty percent deviation is common. Plan around the lower end of each range rather than the upper — the margin you leave is your room for error.
At 4K 60p and the 85-minute lower bound, one pack covers two 40-minute takes with something to spare. That means a morning of four takes needs only one swap per camera. That is the most comfortable rhythm available: fewer swaps, fewer interruptions.
Step three: stagger the swaps
This is the most important rule in the whole plan. If both cameras swap at the same moment, you get a window where both are stopped — precisely the situation you least want, especially when the two angles have to be matched, since realigning timecode after an interruption is a chore.
The method: swap camera A after take two, and camera B after take three. That way, whenever one body is swapping, the other is still recording, and only one camera goes down at a time. The pack that comes out goes straight into a DR-FZ100 slot to recharge, with the second slot reserved for the pack due to come out next.
A schedule you can copy
| Time | Camera A (main) | Camera B (second) | Case status |
|---|---|---|---|
| Take 1, 09:00 | A1 recording | B1 recording | Empty |
| Break, 09:40 | A1 continues | B1 continues | Empty |
| Take 2, 09:55 | A1 recording (margin tight) | B1 recording | Empty |
| Break, 10:35 | Swap to A2, A1 on charge | B1 continues | A1 charging |
| Take 3, 10:50 | A2 recording | B1 recording (margin tight) | A1 charging |
| Break, 11:30 | A2 continues | Swap to B2, B1 on charge | A1 full, B1 charging |
| Take 4, 11:45 | A2 recording | B2 recording | B1 charging |
What matters in this table is not the clock times but the constraint behind them: only one pack charges at any moment. That guarantees the case always has a free slot ready to receive a pack that has just come out, and that you always know exactly how long the other pack has been on charge and roughly where it stands.
Step four: the recharge rhythm
Breaks are usually only ten to fifteen minutes. Taking a pack from low to fifty or sixty percent in that window is realistic; reaching full is not. So do not expect a break to finish a pack — the right expectation is partial top-up between takes, full charge at lunch or after wrap.
The lunch hour is the most effective window. One pack will very likely reach close to full in that time; two depends on the case’s total output, and if the slots share power, charging both is considerably slower than charging one. That is a practical point: at lunch, charging a single pack is often a better use of the hour than loading both.
If your packs are TNP-FZ100 units with a built-in USB-C port, there is a further option: a pack that comes out need not go into the case at all — plug it into a power bank and leave the case free for the other one. You have effectively gained a third charging position. On long location days this combination is very practical, and the FX3 power article covers the underlying approach.
Details that catch people out
- Never swap mid-take. A pack reading 15% can hit the warning within minutes. Put swaps in the breaks and do not gamble.
- Confirm the pack is seated before you walk away. A pack that is not latched may still light the indicator while not actually charging, and you only find out when you fit it and it is empty.
- Let a hot pack cool first. After continuous recording the pack surface is warm, and going straight into a closed case stacks the heat. Give it five minutes, or charge with the lid open.
- Log how each pack performs. Note on your phone that A1 lasted to the end of take two with one bar left; after a few takes your estimates correct themselves.
The value of a rota is that it absorbs uncertainty in advance. At the scale of four packs, two bodies and four takes, getting numbering and staggering right means almost no on-the-spot decisions. More detail is in the DR-FZ100 category, and judging pack condition is covered in the direct-charge battery category.
FAQ
Are four packs enough for a full day of two-camera work?
At four takes a day of forty minutes each in 4K 60p, usually yes, but without much spare. With more takes, longer ones, or 4K 120p, go to six packs or add external power to the fixed camera. The test is whether you can hold the state of two packs in use, one charging and one full at the start of every take — if you can, you have enough; if not, add packs.
Can the two cameras share packs?
Physically yes, but it is better not to swap them mid-shoot: it breaks your runtime expectations and levels out the wear curves. Swap only in an emergency, then update the numbering notes afterwards.
Can the case sit next to the cameras?
Yes, with two cautions: do not put it on the floor where it can be kicked, and do not press it against equipment that runs hot. A partly open lid helps heat escape but lets dust in, so on a dusty set keep it closed and top up back at the hotel.
Why stagger the swaps rather than doing both at once?
Swapping both saves you a few movements and costs you the risk of both cameras being down together. On a two-camera shoot the angles usually complement each other, so a simultaneous interruption means that stretch exists on neither card. Staggering costs two extra minutes and guarantees at least one camera is always recording, which is the better trade.