Short answer: they are not interchangeable. The DR-FW50 bays are molded to the length, width and thickness of the NP-FW50, and the NP-FZ100 is clearly larger, so it will not fit. The reverse is just as wrong: an FW50 in an FZ100 bay sits loose and the contacts do not line up. These are two independent battery systems with their own matching cases, and there is no universal bay. If you need both, the right answer is two cases, not a workaround.
The question usually comes up during a body upgrade: you shot an A6400, later added an A7 body or an A6600, and now own two battery systems. Can one case cover both? No — but understanding why is more useful than memorizing the conclusion.
The difference starts with the battery
The NP-FW50 is a small battery at 1020mAh / 7.7Wh / 7.2V, shaped fairly flat so it could fit the compact bodies of the A6000 series and the early A7 models. The NP-FZ100 was designed for larger bodies, with capacity and volume a step up and thickness especially obvious.
A charging bay is not just a recess that something drops into. It has three parts that must fit precisely: the guide rails on each side, the spring contacts at the bottom, and the latch above. All three are designed for one specific battery outline. A millimeter off and the contacts no longer press where they should.
So bay compatibility is not a question of “roughly the same size” but of “was this mold cut for this model.” The DR-FW50 answers only for the NP-FW50 series; the DR-FZ100 answers only for the NP-FZ100 series.
Size and bay comparison
| Point of comparison | DR-FW50 | DR-FZ100 |
|---|---|---|
| Battery supported | NP-FW50 series | NP-FZ100 series |
| Battery outline | Flatter and narrower | Wider and thicker, a size up overall |
| Bay depth | Cut to FW50 thickness | Deeper, to take a thicker battery |
| Contact position | Matches FW50 bottom contacts | Matches the FZ100 contact layout |
| Result of mixing | FZ100 will not fit, or only goes in at an angle | FW50 sits loose and fails to register |
The word “angle” in that table deserves its own paragraph. Some people lay an FZ100 diagonally into an FW50 bay so one edge barely touches, and the light flickers on occasionally. That state neither charges the battery nor avoids permanent stress on the contacts at an angle — the worst of both outcomes.
Three consequences of forcing it
- It will not charge, and you will blame the battery. With the contacts misaligned the case cannot detect the battery, so no light comes on. Plenty of good batteries have been written off as faulty this way.
- The contacts deform. Repeated angled insertion permanently bends the spring contacts, and even the correct battery will then make poorer contact. This damage is irreversible.
- The shell and latch take damage. Forcing the lid shut loads the battery casing, which at best scratches and at worst deforms it — and a deformed casing can make poor contact inside the camera.
Of those three, the first is a misdiagnosis and the last two are real damage. Saving the price of one case can cost you a battery plus a case, which is a poor trade.
What to do if you run both systems
- Two cases, each independent. The DR-FW50 handles FW50 batteries, the DR-FZ100 handles FZ100, each with its own cable. Do not cross them.
- Distinguish them by color or label. A strip of different-colored tape on the outside is enough to tell them apart in low light and avoid a wrong load at midnight.
- Mark the batteries too. Prefix FW50 batteries with F and FZ100 with Z, and put a matching note inside the camera’s battery door.
- Allocate by body when traveling. Bring the case for the body you are bringing, not both, so you are not carrying dead weight.
If you truly can only bring one case, bring the one for your main body, and top up the other system’s batteries through a direct-charge version such as the YO TNP-FW50, which has its own USB-C port. That is the most practical value of direct charging in a mixed kit.
One last warning: do not count the A6600 as part of the FW50 family. This is the easiest mistake to make. The A6000, A6300, A6400, A5100, ZV-E10, the NEX series, the RX10, and the A7 and A7 II all use the NP-FW50; the A6600 uses the NP-FZ100 and sits outside this system.
Which means “the whole A6000 series uses FW50” is simply false. Before buying a battery, a case or a spare power source, check against the specific model rather than inferring from the series name. For the FZ100 system see the FZ100 category page; for the FW50 case see the DR-FW50 category page.
Note also that the FZ100, being larger in capacity, does not behave identically to the FW50 in cold conditions; there is a separate test record at the NP-FZ100 cold-weather test, but it applies only to the FZ100 and cannot be projected onto the FW50.
FAQ
Can the DR-FW50 charge an FZ100 battery?
No. Both bay size and contact position are wrong, so the battery cannot reach the correct position and the case will not detect it. Forcing it in at an angle risks damaging the contacts.
Can the two cases share a charging cable?
The cable itself is usually shared, as long as the connector type matches and the supply is adequate. Do not run both cases from one splitter at the same time, though; the supply tends to sag and detection becomes unreliable.
What happens if I put an FW50 in an FZ100 case?
The bay is too wide and too deep, so the battery sits loose and cannot press on the contacts; in most cases no light comes on. Even if contact is briefly made, movement will interrupt charging.
Which battery does the A6600 use?
The NP-FZ100. This is the most frequently misreported detail in the lineup — check the model when buying rather than reasoning from “Alpha 6000 series.”