Short answer: small-capacity packs tend to swell first because they pack a higher energy density into the same space, have less surface area to shed heat, and are often stored full and warm. Prevention comes down to three things — keep the stored charge at 40%-60%, avoid heat, top up every three months, and do not leave the pack on a charger indefinitely. Once it has swollen, stop using it no matter how slight the bulge, and do not attempt a repair.
Swelling is the outcome users can see, but the cause begins months earlier. Understanding where the gas comes from is more useful than memorizing a list of prohibitions, because it lets you judge for yourself which habits accelerate it.
How swelling happens
A lithium-ion cell contains electrolyte that carries lithium ions in normal operation. When the cell spends long periods under adverse conditions — full charge, high temperature, overcharge, deep discharge — the electrolyte decomposes at the electrode surfaces and releases gas (commonly carbon dioxide, alkanes, and hydrogen). Inside a sealed case the gas has nowhere to go, pressure rises, and the case is pushed outward.
At the same time, the SEI layer on the anode keeps thickening, consuming available lithium ions and showing up as capacity loss. Swelling and capacity fade are therefore usually two results along the same path; swelling is simply easier to see.
Why small packs swell first
Higher energy density. Packing more energy into the same volume means thinner, tighter electrodes and denser electrolyte filling, which leaves less room for byproducts. A small amount of gas is enough to visibly distort the case.
Less cooling area. Volume shrinks with the cube while surface area shrinks with the square, so a small pack has a larger surface-to-volume ratio but a smaller absolute radiating area, and heats up faster for the same heat generated. The NB-13L holds only 4.5Wh, and in a small body like the G7X or SX740 it sits right against the processor and the screen, so its working temperature is not low.
More likely to be stored full. This is a habit issue. A small pack charges quickly, so many people top it up right after shooting, drop it back in the bag, and take it out full next time. Large packs charge slowly, which makes long full-charge storage less common.
Four closing steps before storage
- Bring the charge down to about half. If it is freshly full, put it back in the camera and shoot for a while to drain it. Do not discharge it by shorting contacts or repeated insertion.
- Take it out of the body. Left in the camera, standby current slowly drains the pack and the contacts stay under pressure.
- Inspect the case and clean the contacts. Press gently on both sides and feel for springiness or a dent that stays. If you find one, do not store it — treat it as swollen. A dry cloth is enough for the contacts.
- Store it separately, insulated, with the date marked. Use a case or a sealed bag, never mixed with metal objects. Write the last date of use and check and top up three months later.
Storage conditions at a glance
| Condition | Recommended | Avoid |
|---|---|---|
| Charge level | 40%-60% | Full charge, or drained to auto-shutdown |
| Temperature | 15℃-25℃, cool and dry | In a car, near a radiator, in direct sun |
| Container | Insulated case, stored separately | Loose with keys and coins, bare in a drawer |
| Top-up interval | Check every three months and bring to about half | Left alone for a year |
| Charger | Unplug once full | Left in the dock indefinitely |
What to do when you find swelling
The first step is to stop all charging and discharging. Do not try to puncture the case to release gas — the electrolyte inside can ignite on contact with air, and a puncture breaks the seal and triggers further reaction. Do not press it flat with a weight and do not freeze it. None of that removes the gas, and all of it adds risk.
The second step is to isolate it. Keep it on its own away from flammable material, do not stack it with other packs, and do not leave it in the camera while it is swollen. If the case is clearly deformed, if there is an odor, or if it is warm, handle it with extra care.
The third step is recycling. Take it to a local waste-battery collection point or an electronics recycling channel. Do not put it in household trash.
Note that early swelling may only show as a slightly uneven case that is hard to spot by eye. The daily check is simple: lay the pack flat on a table and see whether all four corners sit flush and whether it rocks; or pinch both sides gently and feel for abnormal springiness. A healthy pack should be firm and should not give.
FAQ
Can a slightly swollen pack still be used?
Not advisable. Swelling is an irreversible structural change, and continued use keeps generating gas, so the risk only increases. Even a slight bulge means retire it and recycle it as soon as possible.
Is a slightly bulging new pack normal?
No. A new NB-13L II should be flat, firm, and flush at all four corners. If it arrives swollen, that is a quality defect — contact the seller for a replacement and do not use it.
Will a dry cabinet prevent swelling?
A dry cabinet solves humidity, while swelling is driven mainly by charge level and temperature. Low humidity helps, but a full pack in a warm cabinet will still swell. Charge level and temperature are the levers that matter.
Does brand affect swelling?
It matters, but it is not decisive. Low-grade cells and products without a protection board carry higher risk, and reputable brands — including YO’s NB-13L II — are more disciplined in cell screening and protection design. But even a good pack will swell if stored full and warm for long periods. For storage guidance see the NB-13L II category, and for OEM specs see the NB-13L category.