A power bank swells when gas builds up inside its lithium-ion cells from heat, overcharge, aging, or damage.
Quick note: If your pack is bulging, stop using it now. Unplug it, place it on a non-flammable surface, and arrange safe disposal.
What “Swelling” Means Inside The Battery
Portable packs use pouch-style lithium cells. Inside each pouch, solvents and salts move ions between a carbon anode and a metal-oxide cathode. When cells run hot, sit at full charge, or face abuse, side reactions create gas. The pouch balloons to hold that gas. The shell then bows, seams split, and the pack looks puffed.
Gas formation is a wear marker. It often comes with lost capacity, faster drop from 100%, and rising heat during light use. In short, swelling signals a cell that passed safe operating windows or aged out.
Common Triggers And Early Clues
Here are the usual triggers and the signs you may notice. Treat any bulge as a stop sign.
| Cause | What Happens Inside | Clues You’ll Notice |
|---|---|---|
| High Heat | Electrolyte breaks down and releases gases. | Case feels hot or soft; chemical smell. |
| Overcharge | Voltage stays high; cathode oxidizes; gas builds. | Charge hits 100% fast; warms on trickle. |
| Deep Discharge | SEI layer destabilizes; next charge creates gas. | Won’t wake easily; big voltage sag. |
| Fast-Charge Abuse | High current stresses cells with poor cooling. | Warmth during idle; uneven capacity bars. |
| Age And Storage Full | Months at 100% increase decomposition. | Shorter runtime after light use. |
| Physical Damage | Pouch tear or dent triggers hotspots and gas. | Dent, creak, or rattling shell. |
| Poor BMS Or Knockoff Cells | Weak protections allow unsafe voltage/current. | Random shutoffs; swollen cell soon after. |
Is A Bloated Pack Safe To Use?
No. A puffed cell can vent or catch fire if pinched, pressed, or shorted. Do not charge it, do not tape it flat, and do not pierce the pouch. Keep it away from flame, pets, and pockets. Move it onto tile or concrete, air it out, and plan disposal or professional service.
What To Do Right Now
Make It Safe In Three Steps
- Unplug and power off connected gear. Move the pack onto a non-flammable surface, away from paper or cloth.
- Isolate it. A metal pan with sand or clean litter works. Leave space around the pack for air.
- Contact a repair shop or e-waste center for safe handling. Do not ship a damaged cell unless a carrier accepts that class of item.
How To Dispose Without Risk
Local e-waste programs and many repair stores accept swollen lithium cells. Tape any exposed terminals, keep the pack in a cool spot, and carry it in a non-conductive box. Never drop a damaged cell into curbside trash or standard recycling, since compaction can ignite it.
Why A Power Bank Bloats: Plain-English Science
Heat And Full-Charge Stress
Cells dislike extended time above room temperature and parked at 100%. Heat speeds side reactions. High voltage holds the cathode at an energetic state. Pair the two and you get faster gas formation and faster aging.
Overcharge Or Faulty Protections
A good battery management system (BMS) caps voltage and current, balances cells, and shuts down on fault. Cheap units can miss those limits. When voltage runs long at the top of the range, electrolyte oxidation picks up and gassing grows.
Deep Drains And Long Storage
Sitting empty or near empty for weeks disrupts the protective layer on the anode. The next recharge rebuilds that layer and consumes electrolyte, which can make gas. Storing a pack full and warm has a similar effect, just from the other direction.
Physical Stress
Crush, drop, or bending forces can nick a pouch or separator. That spot heats, the chemistry degrades, and a bulge follows. Once a case warps, even gentle pressure in a bag can worsen the tear.
Prevention That Actually Works
Charge Habits That Cut Risk
- Top up between 20% and 80% for daily use when convenient.
- Skip leaving the pack on a wall charger overnight.
- Let the pack rest after fast charging before heavy use.
Smart Storage
- Store around half charge in a cool, dry drawer.
- Avoid cars, heaters, windowsills, and direct sun.
- Cycle the pack every few months if it sits unused.
Pick Safer Hardware
Look for third-party safety marks and a clear model number. UL-tested units list “UL 2056” with a file number. Reputable brands publish watt-hour ratings and cell specs. Knockoffs hide that data and often skip protections like thermal fuses.
Travel Rules And Safe Carry
Portable chargers count as spare lithium-ion. Airlines keep these in cabin bags so crews can respond to incidents. Check watt-hour limits, keep ports covered, and never pack a damaged unit. If a pack swells on a trip, tell a crew member and keep it isolated in view.
For policy details, review the FAA’s PackSafe lithium battery rules. For product safety testing, see UL’s UL 2056 overview.
When A Warranty Or Recall Applies
Brands sometimes recall packs after heat or fire reports. If yours matches a recall model, stop use and contact the brand for a remedy. Keep serial and proof of purchase ready. Do not mail a swollen pack unless the return kit includes a compliant hazmat box.
Do/Don’t Checklist When A Pack Bloats
| Action | Why It Matters | How-To Snapshot |
|---|---|---|
| Stop Using It | Charging or load can trigger venting. | Unplug, power off, isolate on tile. |
| Shield The Terminals | Prevents short circuits during transport. | Cover ports; bag the pack separately. |
| Seek Pro Disposal | Waste sites handle fire risk properly. | Call e-waste or a repair shop first. |
| Do Not Puncture | Piercing can cause fire and toxic fumes. | Leave the pouch intact at all times. |
| Do Not Flatten | Pressure can rip the pouch seam. | Never clamp or tape the bulge. |
| Do Not Ship Illegally | Damaged cells may be restricted. | Use only approved return kits. |
How To Tell Swelling From Flex
Cosmetic Flex
Thin plastic shells can creak when twisted. That kind of flex vanishes when you set the pack on a flat table. No smell, no warmth, and sides stay flat.
True Bulge
A real bulge changes the silhouette. The case rocks on a table, seams gap, or buttons feel stiff. You may notice a sweet solvent scent. Treat that as active risk.
Charging Math In Plain Terms
Output power equals volts times amps. A 20-watt phone charge at 5 volts pulls about 4 amps. Higher wattage raises heat. Heat speeds breakdown, so quick charge modes are best saved for short bursts. For daily use, a gentler rate keeps temperatures in check.
Capacity ratings use watt-hours. A pack labeled 37 Wh holds roughly 10,000 mAh at 3.7 V inside the cells. Step-up losses cut what reaches your device. Hot weather or thick cases can add losses too.
Care Myths That Hurt Cells
- “Draining to zero helps.” Deep drains strain the protective layer on the anode and can lead to gas during the next charge.
- “Leaving it plugged in is harmless.” Sitting full for days promotes side reactions and puffing.
- “Flattening a bulge fixes it.” Pressure masks the symptom and raises fire risk.
- “Freezing will reset it.” Moisture and low temps can crack seals and damage the pouch.
Buying Checklist For Safer Packs
- Clear Specs: Look for watt-hours, cell type, and charge input limits on the label.
- Safety Marks: UL 2056 listing with a file number beats vague badges.
- Thermal Design: Vents or spacing around cells help shed heat during fast charge.
- Protections: Over-voltage, over-current, over-temp, and short-circuit protections should be listed.
- Authentic Seller: Buy from the brand or trusted retail channels to avoid sketchy cells.
When It’s Time To Retire A Pack
Retire the pack at the first hint of bulge, repeated thermal shutdowns, or a sharp drop in runtime. Packs also age on the shelf. If a unit from a drawer charges slow, warms during idle, or smells odd, send it to e-waste.
Signs Of Trouble You Shouldn’t Ignore
Visual And Tactile Red Flags
Gap between shell halves, wavy sides, creaks when pressed, or a rubbery feel all point to internal pressure. Any sweet, solvent-like smell is another cue.
Performance Hints
New heat during light loads, sudden shutdowns, or a jumpy meter suggest stressed cells. If the pack warms while idle, retire it.
How We Built This Guidance
This guide pulls from peer-reviewed work on gas generation in lithium cells, long-running industry education on cell care, and safety standards for portable chargers. We cross-checked practical steps against repair community best practice and consumer safety alerts.
Helpful Resources
You can review the FAA’s PackSafe lithium battery rules and UL’s UL 2056 standard overview for more detail on safe carriage and product testing.