Short answer: with one pack the two are close — Sony’s BC-QZ1 is rated at roughly two and a half hours, and a single DR-FZ100 slot takes about 2.5 to 4 hours. With two packs the gap opens immediately: the BC-QZ1 has to queue, doubling total time past five hours, while the DR-FZ100 runs both slots at once and finishes in about 3 to 5 hours. What you save is roughly one pack’s worth of charging time. The more packs you own, the wider that gap becomes. Below is the arithmetic, and the price the dual-slot design pays for it.
Running the numbers
A single dock is serial by nature: one pack finishes before the next begins. A dual-slot case is parallel: both start together and finish independently. So the difference is not a fixed number of minutes — it scales linearly with how many packs you are charging.
| Packs | BC-QZ1 (serial) | DR-FZ100 (parallel) | Approximate gap |
|---|---|---|---|
| 1 | About 2.5-3 hours | About 2.5-4 hours | Effectively level |
| 2 | About 5-6 hours | About 3-5 hours | Saves around 2 hours |
| 4 | About 10-12 hours | Two rounds, about 6-9 hours | Saves 3-4 hours |
Note one detail in the second and third rows: when both slots run, the input power is split between them, so each pack charges a little slower than it would alone. Total time is therefore not exactly one pack’s time — it usually runs half an hour to an hour longer. That is the inherent cost of parallel charging, and every dual-slot product behaves the same way.
Why it is not ahead with a single pack
If you only ever use one pack a day, a dual-slot case has nothing to offer. With all the power going to one slot it behaves much like any other charger, and may even be marginally slower than an open dock because the body is more compact and the heat path longer. In that situation a single dock, or simply charging the pack through its own USB-C port, makes more sense.
The value starts with the second pack. Anyone running two or more packs and emptying them every day is the target user. The test is straightforward: if you own two or more packs and tend to charge them all in the evening, what you save is a real two hours of sleep.
Four differences beyond time
Power source: mains versus USB
The BC-QZ1 runs on mains, so you need a socket, and traveling means carrying a fairly bulky power supply. The DR-FZ100 takes USB input, which means a phone charger, a laptop’s USB port, a car adapter, or a large power bank. That means it still works where there is no socket — in the car, in the field, in a makeshift rest area.
Size and portability
A dock plus a power supply is two objects, and the cable goes its own way. The dual-slot case is a single unit: close the lid and it is a storage box, and the packs travel inside it. For anyone moving between locations, one less loose item is one less thing to hunt for.
Storage is folded into the same object
This part is often underestimated. A dock only charges; once the pack is full it still needs somewhere to live. The dual-slot case makes the charging position and the storage position the same space: drop the packs in at the end of the day, close it, pack it, and open it the next morning to full batteries. Three steps become one.
A different cost structure
An OEM dock is sold as a separate accessory at a fairly high price; the dual-slot case is positioned as the alternative, so the outlay is clearly lower. For anyone who needs two packs or more, what you save is not only money but the attention spent double-checking whether the dock made it into the bag.
When a single dock still wins
Three situations. One: a single pack covers everything and light travel matters most. Two: you already own an OEM dock and do not mind the queue, in which case a case is duplicate spending. Three: you only charge OEM packs and have firm expectations about the charging curve, where first-party accessories will always match best.
Conversely, two kinds of user should go straight to the dual-slot case: people shooting two or more cameras who produce a lot of material each day and need to start the next morning full, and people who travel often with uncertain accommodation and few sockets. The second group’s pain is sockets, not time — one USB port covers two packs and a phone at once, which a dock cannot do.
More flexible with direct-charge packs
If your packs are TNP-FZ100 units with their own USB-C port, you end up with three charging routes: the case doing everything overnight, charging in the camera body, and a single pack running off a power bank. The three back each other up, so losing any one of them does not derail the next day.
That is also why a dual-slot case and direct-charge packs are often recommended together: they solve two ends of the same problem — the case handles volume, direct charging handles mobility. Product details are in the dual-slot charger section.
FAQ
How much slower is charging two packs than one?
Usually half an hour to an hour slower. The input power is shared across both slots, so the current reaching each pack drops. A USB supply with a higher output current narrows that gap.
Can I use the dock and the case side by side?
Yes, they do not interfere. Some people keep the OEM dock at home as a fixed station and carry the case in a bag; the case handles life on the road and the socket handles home. That gets you the strengths of both.
Does a dual-slot case wear batteries out faster?
No. Parallel charging only divides the total power, so the current each pack sees is actually lower, which is gentler on the cells. What really affects service life is heat and long-term storage at full charge, neither of which depends on how many slots you have.
What is the fastest way to handle four packs?
Load two in the evening, swap in the other two when they finish; the second round usually completes before bedtime and all four are full by morning. If you only have three or four hours, charge the two you need first the next day.