Direct answer: a mildly warm NP-FZ100 on charge is normal; too hot to hold for more than a second or two is not. Charging a lithium cell is an energy conversion, and some of that energy leaves as heat, especially during the bulk phase where current is highest. A rough hand test: if the pack feels warm and you can keep it against your palm, that is within the normal range. If you pull your hand away, or the charger shell is too hot to touch, cut the power and investigate. These are practical guidelines rather than a measured temperature standard — your own product documentation and common sense come first.
Where the Heat Comes From
- Conversion losses: cell internal resistance turns part of the incoming energy into heat during constant-current and constant-voltage charging. This cannot be avoided entirely.
- Charge current: higher current fills the pack faster and produces more heat per minute. A multi-bay charger running several packs at once runs warmer overall.
- Ambient conditions: a hot room in summer, or a pack charging inside a camera bag or under a blanket, has nowhere to dump heat, so it accumulates.
- Ageing: as a pack approaches roughly 300–500 cycles, internal resistance rises, so the same current produces more heat than it did when new.
So “hot while charging” covers two very different situations: a new pack on a ventilated desk, and an old pack sweating inside a closed bag.
Hand Test: Where Normal Ends
| How it feels | Likely state | What to do |
|---|---|---|
| Barely warm, just above room temperature | Trickle stage or about to go green | Normal. Let it finish |
| Warm, comfortable against your skin | Typical mid-charge condition | Normal. Keep it ventilated |
| Hot enough that you want to let go after a few seconds | High, worth checking | Unplug, let it cool, check charger and placement |
| Too hot to touch, with smell, noise or case deformation | Fault, safety relevant | Cut power, move it to open space, stop using it |
Hand feel is subjective and depends on room temperature. When in doubt, change one variable: a different charger in a different spot. If it runs noticeably cooler, the original charger or its location was the problem.
Six Ways to Keep Charging Temperatures Down
- Charge on a hard, flat, ventilated surface. Not carpet, not a bed, not inside a camera bag.
- Keep it out of direct sun and away from radiators and hobs. A warm room stacks on top of charging heat.
- Do not chase speed with high current. Routine-rate charging is kinder to cells.
- Leave space between packs on a multi-bay charger. Do not stack chargers or cover them.
- A pack straight out of the camera is already warm. Give it a few minutes before it goes on the charger.
- Let the charger reach its green “done” state before pulling the pack, instead of interrupting the bulk phase repeatedly.
Signals That Mean Stop Immediately
- Swelling, deformation or a case splitting at the seam — stop using it and do not charge it again; handling is covered in what to do with a swollen battery.
- Burning smell, smoke or unusual noise — cut power, move the pack to a clear dry area away from anything flammable.
- A charger that is itself too hot to touch, discoloured or scorched — retire that charger and check the spec matched.
- Charge level that goes backwards, or a pack that never finishes — swap the charger and the pack one at a time to isolate which is at fault.
- A pack that is full and then flat within minutes, or shutdowns mid-shoot — that points at a worn cell rather than a charging fault.
Heat Outside of Charging
Batteries also warm up in the camera during long video takes and fast burst shooting. That is discharge-side heat, different from charging heat but worth the same attention. If the body is clearly warming during continuous 4K, rotate packs so each one gets a cooling break, or move to a dummy battery with an AC adapter. The options are set out in uninterrupted power for video and streaming. Cold is the opposite problem: a chilled pack loses usable capacity, and the fix starts with keeping spares in an inside pocket.
Two Safety Notes
First, do not put a pack in the fridge or cool it with water to make it “less hot”. Condensation risk outweighs any benefit. Second, when buying, look at cell spec, protection circuitry and whether the charger actually matches — that reduces heat problems far more reliably than shopping for a slower charger. The reasoning is in third-party battery safety.
FAQ
A brand-new pack runs hot on its first charge. Is it faulty?
Rule out environment and charger first: move it to a ventilated desk, then try a different charger. If it still runs clearly hot, ask the seller for a replacement and do not open the pack yourself.
Does charging heat damage the cells?
Sustained high temperature accelerates capacity loss. Occasional warmth has limited effect, but storing a pack full in a hot place will age it noticeably faster.
Does it keep heating if I leave it plugged in?
Heat drops off once charging reaches the trickle or done state, but leaving a pack at 100% indefinitely is not a good habit. Take it off the charger when it is done, and store long-term at roughly 40–60%.
Is fast charging worse than slow?
High current runs hotter and has a small long-term effect on ageing. Use routine current when you are not in a hurry, and save fast charging for when you are.
A matched charger removes most of the guesswork. YO’s NP-FZ100 compatible battery is rated around 2280mAh / 7.2V / 16.4Wh, at about $17.89 for a single pack, about $22.93 for one battery with a charger and about $36.74 for two batteries with a charger — the bundled charger is specified for these cells. The TNP-FZ100 is the 2400mAh / roughly 17.3Wh alternative. Studios and rental houses kitting out batteries and chargers together should go through wholesale enquiry, where orders over 100 units are quoted per batch.