Short answer: capacity fade in a lithium-ion pack like the TNP-FZ100 is gradual, typically falling to about 80% of rated capacity after 300–500 full cycles; whether to replace comes down to how many fewer frames it delivers in the same situation, and whether charging heat and charging time have visibly changed — you do not need to wait until it refuses to charge at all. The method below needs no instruments and no disassembly; ordinary shooting records are enough.
One thing to be clear about: this article will not give figures like “after X months it is at Y percent”. Fade correlates strongly with depth of discharge, ambient temperature, storage charge level and discharge current, so any single sample’s numbers say little about anyone else’s. What can be given is the mechanism, the ranges and reproducible checks.
How fade happens
Capacity loss in a lithium-ion cell comes mainly from three places: structural fatigue in the cathode material, progressive thickening of the solid electrolyte interphase on the anode, and slow decomposition of the electrolyte. All three accumulate with cycles and are accelerated by heat. For a 7.2V / 2280mAh / 16.4Wh specification like the NP-FZ100, the two most direct variables are depth of discharge and temperature.
Running the pack to auto-shutdown before recharging wears it noticeably faster than topping up at twenty or thirty percent. Equally, leaving packs in the car in summer, or dropping a hot camera straight into a sealed bag, steepens the fade curve early. That is why two packs bought in the same batch can be in quite different states a year later.
Because the TNP-FZ100 charges over USB-C with the charging circuit in the pack itself, the effect of long, hot charging is worth more attention than with a dock — if it feels hot in the hand while charging, switch to a gentler charger or move it somewhere with airflow.
Three checks that need no instruments
Method one: count frames in the same situation
Fix one scenario — the same event, the same burst ratio, the viewfinder used or not — and count the frames between a full charge and the low-battery warning. The number a new pack delivers in that scenario is your own baseline. Repeat every two or three months; if the figure falls below seventy percent of baseline, fade is affecting real use.
Do not mix numbers from different scenarios: LCD versus EVF, stabilisation on or off, and burst ratio can each move the count by twenty or thirty percent.
Method two: watch charging time and heat
Rising internal resistance accompanies fade. It shows up as a shorter charge from low to full — because less capacity is actually going in — but with more noticeable heat, concentrated in the middle of the pack. A distinctly shorter charge combined with a hotter shell than before usually means the fade is no longer slight.
Method three: look at the shape of the discharge curve
A healthy pack falls fairly evenly. One with obvious fade often holds steady and then plunges: from 30% straight to the warning, or losing a bar soon after coming off a full charge. That non-linear drop is typical of elevated internal resistance, appears earlier than the loss of total capacity, and reflects the real state more honestly.
When you must replace, and when you can keep it
| What you observe | What it usually means | Recommendation |
|---|---|---|
| Frames down to about 70% of a new pack, still falling evenly | Normal fade, now in its later stages | Keep as a spare, no longer for the main camera |
| Jumps from about 30% straight to the warning | Internal resistance clearly elevated | Demote to short pickups and replace soon |
| Shell visibly swollen while charging, will not seat in the bay | Gas formed inside, a safety concern | Stop using at once, do not charge again |
| Voltage falls very low after a week at full charge | Abnormal self-discharge | Retire it, do not take it out of the house |
| Charger gets hot and restarts repeatedly | Fault in the charging circuit | Test with another charger first, replace the pack if it persists |
The first two rows of that table are still usable; the last three are safety matters and should not be stretched. Swelling is the least negotiable signal — once a lithium pack has swollen, the internal chemistry is out of control, and continued charging carries a fire risk regardless of how much capacity is left.
How to slow the fade
- For long storage, leave the pack at forty to sixty percent rather than full or empty across the season. Full storage accelerates cathode ageing, and empty storage risks over-discharge and sleep.
- Avoid charging in hot places. A summer car or a sunlit windowsill is not suitable.
- There is no need to drain it flat every time. Shallow cycling is kinder to cycle life; lithium cells have no memory effect.
- Charge before you travel, not a week in advance. For cold and heat precautions, see our notes from minus ten degrees.
A rough guide by intensity: two or three shoots a week at one or two hundred frames each, and two or three years from a pack is normal; with daily high-rate bursts or long recordings you will notice faster drain in about eighteen months. On this measure the YO TNP-FZ100 behaves no differently from an original pack of the same specification.
FAQ
My new TNP-FZ100 seems to last less than the original — is it fading?
Usually not. A new pack has not faded appreciably; the difference is more likely in how the rated capacity is calibrated, in the body’s estimation strategy for third-party packs, and in the fact that you compared under different conditions. Run method one above in a fixed scenario for each, then judge. Body estimates of third-party packs are also often non-linear, so a low percentage does not necessarily mean little charge remains.
Can I measure capacity myself?
Roughly. Charge the pack from low to full on a USB charger that displays wattage, note the Wh delivered, and multiply by charging efficiency (usually estimated at 0.8–0.9) to work back to usable capacity. The method has preconditions: the same starting charge, a similar ambient temperature, and an accurate readout on the charger. The error is not small, so it is good for trends, not for firm conclusions.
Must I replace at 80%?
Not necessarily. Eighty percent is the conventional threshold used to describe cycle life in the industry, not a threshold for use. If your workload is modest and the situations are controlled, a pack at eighty percent still works as a spare. The real dividing line is whether it still affects your shooting rhythm, and whether swelling or abnormal heat has appeared. The rules for flying with batteries are in this guide, and they apply equally to a faded pack.
Two packs bought together — why do they fade at different rates?
The usual reason is different intensity of use: one sits in the main camera and is often run deep, the other only comes out occasionally. Next is charging habit, for instance one regularly on a high-power charger and the other on an ordinary one. Number the packs and rotate them, and their fade will converge.