Short answer: on 5V input, a 5V/2A charger typically takes a TNP-FW50 from empty to full in 1.5 to 2 hours, while a 5V/1A charger takes roughly 2 to 3 hours — about an hour apart. That gap does not keep scaling with power, though: the charging circuit inside the pack caps the maximum current, so a stronger charger can only feed it up to that ceiling. Buying a bigger charger therefore has a clear limit to what it can return.
The TNP-FW50’s cells hold 1020mAh / 7.7Wh, which is a small capacity. The advantage of a small pack is fast top-ups; the disadvantage is that its useful sensitivity to input power is narrow — going from 1A to 2A is noticeable, going above 2A largely is not.
Where the numbers come from: theory versus reality
Start with a rough sum. A 7.7Wh pack on a 5W input (5V × 1A) would fill in about 1.5 hours in an ideal world; on 10W (5V × 2A) it would take under an hour. Real charging is not ideal, and three things eat into that.
- Conversion losses: 5V has to be stepped down to cell voltage, and the charging circuit itself warms up, so efficiency typically lands around seventy to eighty percent.
- The constant-voltage phase slows things down: above about 80% the pack switches to constant voltage, current tapers, and the last 20% often consumes forty percent of the whole process.
- Cable drop: thin or long cables lose noticeable voltage at higher currents — the charger reads 5V while the pack sees perhaps 4.7V, and the circuit reduces current in response.
Allow for those three and 2 to 3 hours on 5V/1A and 1.5 to 2 hours on 5V/2A are sensible ranges. It also explains why so many people swap in a 2A charger and find it is nowhere near twice as fast: losses and the constant-voltage phase absorb most of the difference.
The two inputs side by side
| Input | Theoretical power | Empty to full | Where it fits |
|---|---|---|---|
| 5V/1A (basic charger, old car adapter, computer USB port) | 5W | About 2-3 hours | Overnight, casual top-ups at a desk |
| 5V/2A (mainstream phone charger, most power banks) | 10W | About 1.5-2 hours | Between takes, hurrying before you leave |
| 5V/3A or a PD charger (still 5V after negotiation) | Draw at the 5V tier | Close to 2A, little gain | Not worth buying for this pack |
The third row is worth a sentence. The TNP-FW50 takes a standard 5V input and does not negotiate high-voltage fast-charge protocols, so plugging in a 65W PD charger just means it draws at 5V, and how much current it gets is set by the pack’s own limit. In practice the phone charger you already own is enough, and there is no need to buy a “fast charger” specifically for this battery.
The pack sets the current ceiling
This is widely misunderstood: people assume a more powerful charger means faster charging. In the constant-current phase, how much current actually goes in is decided by the charging management chip inside the pack; the charger only sets an upper bound on what is available. When the pack limits itself to around 1.2A, a 2A or 3A charger gives much the same result.
So between 5V/1A and 5V/2A the difference is real, while between 5V/2A and 5V/3A it is marginal. If your goal is saving time, replacing an old 1A charger with a 2A one works; replacing 2A with 3A does not.
What to actually choose: three suggestions
- One 5V/2A charger is enough on the road. It can feed a phone and the pack, and it is not bulky. Multi-port chargers are handier still, though watch that a single port is not being asked to share too much of the total.
- Cables let you down more often than chargers. Choose 20AWG or thicker and keep the length under a meter; the thin, soft cables bundled with devices drop noticeable voltage at higher currents.
- In a hurry, stop at eighty percent. The constant-voltage phase is where the time goes: 0 to 80% takes roughly half the total, so there is no need to wait for a full pack on location.
If you are charging the night before a trip, a 1A charger is perfectly adequate — plug in, go to sleep, and it is full in the morning. The scenario that genuinely calls for 2A is having an hour before you leave with an empty pack, and that is when the difference earns its keep.
Power banks and car adapters
With power banks, a common 10000mAh unit will fill a 7.7Wh pack three or four times over, but check that its output port supports 5V/2A auto-detection. Plenty of older banks only offer 5V/1A, which means slow charging the moment you plug in.
With car adapters, voltage fluctuates sharply as the engine starts, so plug in after the engine is running. Leaving packs in a hot car for long periods affects capacity far more than charging speed does — that matters more than which charger you pick.
If you often need to charge two packs at once, plugging cables in one at a time gets tedious; a dual-slot case is the smoother option, covered under the DR-FW50 dual-slot charging case. The list of compatible bodies for the pack itself is on the TNP-FW50 category page.
FAQ
Does charging at 5V/1A harm the pack?
No. Lower current is gentler on the cells and generates less heat; it is simply slower. What actually affects service life is heat and long-term storage at full charge, not slow charging.
Why is my 2A charger as slow as a 1A one?
Try a shorter, thicker cable first — most cases are cable drop causing the circuit to reduce current on its own. If a different cable changes nothing, the charger may be sharing its output across several ports at once.
Can I charge from a laptop’s USB-C port?
Yes, as long as the port supplies 5V. Some laptops cut power to their USB-C ports when asleep, which stops charging halfway, so avoid charging with the lid closed and the machine sleeping.
Does it stop automatically when full?
A properly designed pack switches to a trickle and then stops, so leaving it connected will not keep overcharging it. As a habit, unplugging once it is full is still safer and avoids pointless warmth.