If your e-bike battery is swollen, cracked, leaking, unusually hot, smoking, hissing, or making a chemical smell, do not plug it in. Disconnect the charger only if it is already safe to touch, move people away from the area, and treat the battery as a fire risk until a manufacturer or qualified authority tells you otherwise. The U.S. Consumer Product Safety Commission (CPSC), the organization that writes the safety standards for e-bike electrical systems, both treat these signs as stop-use triggers, not situations to test with a charger.
This is not a repair guide. Nothing here tells you how to fix, open, or diagnose a battery yourself. It tells you when to stop, how to stay safe while you figure out what happened, and who to contact next.
When Charging Is Not Safe
A lithium-ion battery that shows physical or behavioral abnormalities is signaling internal cell damage, which can progress to thermal runaway — an uncontrolled heating reaction that can escalate to fire with little warning. Do not charge, ride, or continue using the battery if you observe any of the following:
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The casing looks swollen, bulging, cracked, dented, or otherwise deformed compared with its original shape.
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Liquid or residue is leaking from the casing, or you see corrosion, discoloration, or crusty buildup around the terminals or connector.
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The battery feels hot to the touch while sitting idle, not just during charging or riding.
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You hear hissing, popping, or crackling sounds coming from inside the pack.
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There is a strong chemical, sweet, or burning odor near the battery or charger.
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You see smoke, sparking, or scorch marks on the battery, connector, or charging port.
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The connector pins are bent, burned, melted, or otherwise visibly damaged.
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The battery has been submerged in water, dropped, crushed, struck in a crash, or otherwise subjected to a mechanical impact, even if it still appears to power on.
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CPSC, the manufacturer, or a retailer has issued a stop-use warning or recall notice that matches your battery's brand and model number.
Fire-safety authorities across the UK, Australia, and the US converge on the same list: swelling, unusual heat, odd smells, leaking, and hissing or popping sounds are the recognized precursors to a lithium-ion fire, and every one of them is a reason to stop, not a reason to test. None of these signs can be safely evaluated by plugging the battery in "just to check." Charging pushes more energy into a cell that may already be venting gas or breaking down internally, which is one of the electrical stress factors identifies as a direct contributor to thermal runaway.
What Triggers a Manufacturer Contact Instead of a Charge Attempt
Some situations don't show obvious surface damage yet still call for professional evaluation before the battery goes anywhere near a charger.
Impact or crushing. A battery that has been dropped, hit in a crash, run over, or squeezed in transport can have internal cell damage with no visible sign on the casing. UL Solutions lists drops, crashes, shock, and penetration among the mechanical causes of thermal runaway, separate from any external deformation you can see.
Water exposure. Submersion or heavy water intrusion is listed by UL Solutions as an environmental factor that can trigger failure, distinct from ordinary rain resistance a battery may be rated for. A battery that has been fully submerged should be treated as compromised even if it appears to power on normally.
Corrosion at terminals or connectors. Corrosion changes the electrical contact at the connection point and can indicate prior moisture intrusion or seal failure. Do not clean it yourself and try charging again; contact the manufacturer for guidance specific to that battery.
A history of overheating during charging or riding, even if the battery currently feels normal. Aging and repeated thermal stress are cumulative factors in cell degradation, according to UL Solutions' breakdown of failure causes.
Extended storage without manufacturer-specified maintenance, particularly storage in extreme heat or cold, or storage at very low or very high charge for long periods. Follow the exact storage guidance in your battery's manual rather than assuming a long-idle pack is safe to simply plug in.
An active recall or CPSC stop-use warning. CPSC currently maintains active warnings and recalls covering specific e-bike battery models — for example, warnings tied to particular battery model numbers sold with certain Rad Power Bikes models, and recalls affecting VIVI e-bike batteries — and continues to add new notices as issues are confirmed. A recall notice is a stop-use instruction on its own, independent of whether the battery currently shows any visible symptoms; check your battery's exact model number against the current CPSC recall list before you charge it.
If any of these conditions apply and you are unsure, the safe default is to contact the manufacturer or a qualified service center before charging again, not to attempt one trial charge to see what happens.
What To Do Right Now
Follow this sequence rather than improvising a home check:
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Move people, pets, and flammable material away from the battery if you can do so safely. If the battery is actively smoking, hissing, or clearly heating up in front of you, do not pick it up or try to move it — leave the area yourself and get others out too.
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Call emergency services if the battery is smoking, has visible flame, or is rapidly heating in a way that suggests it is already failing. Fire-safety agencies are consistent on this point: once a lithium-ion pack is actively venting or burning, it is a fire department matter, not something to carry outside yourself.
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If the situation is not an active emergency, unplug the charger only if it is already safe to reach, and leave the battery disconnected on a hard, non-flammable surface away from combustible material, walls, and exits.
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Do not attempt to open the casing, puncture it, compress it, tape over damage to hide it, or apply another charger to "test" whether it still works. None of these actions make a compromised battery safer, and using an unauthorized charger or continuing to handle a damaged pack are specifically flagged by UL Solutions as unsafe practices.
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Photograph the battery from a safe distance — the label with model and serial number, and the visible damage — without approaching a smoking or actively venting unit. This documentation helps the manufacturer or CPSC identify the exact battery.
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Identify the battery and charger model from the printed label, and check that model number against the CPSC recall and warning database before doing anything else.
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Contact the manufacturer's support line or a qualified service center for next steps. For TST-brand batteries, TST's support team can confirm whether your specific model and serial number are affected by any active notice.
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Do not put the battery in household trash or ordinary curbside recycling under any circumstances. CPSC is explicit that damaged, swollen, or recalled lithium-ion batteries must go through a household hazardous waste (HHW) collection program, not general trash or standard battery drop-off bins, because they pose a distinct fire risk in waste and recycling streams.
Replacement Only After the Safety Question Is Settled
Once the manufacturer or a qualified authority has confirmed the battery is damaged, defective, or subject to a recall — and only at that point — replacement becomes the relevant next step. If your battery is affected by an active recall, the manufacturer's recall process typically provides the replacement path directly, sometimes at no cost, along with specific disposal instructions for the affected unit. If your battery is not subject to a recall but a qualified inspection confirms it is unsafe to continue using, ask the manufacturer's support team about an authorized replacement battery for your exact model. Never substitute an aftermarket or "universal" charger or a battery not confirmed compatible by the manufacturer; CPSC has separately warned that universal chargers marketed for micromobility devices carry their own fire risk.
Battery identification matters here: a replacement must match your bike's exact model and voltage requirements. Confirm the correct part with TST support or your point of purchase before ordering anything, rather than assuming any battery of similar appearance will fit or charge safely.
Frequently Asked Questions
Does a battery that still turns the bike on but smells odd need to stop charging?
Yes. An unusual chemical or sweet odor is listed by fire-safety authorities as a precursor sign of internal breakdown, independent of whether the bike still powers on normally. Powering on is not evidence the cells are stable.
Is a battery that got briefly rained on the same risk as one that was submerged?
No, but the two are not automatically the same either. Manufacturers rate many e-bike batteries for limited weather resistance, detailed in the specific product manual; full submersion is a materially different exposure and is treated as a potential failure trigger regardless of the battery's weather rating. When in doubt about which category applies, contact the manufacturer with the details rather than assuming either outcome.
If there's no visible damage after a crash, is it still risky to charge?
Yes, it can be. Impact and crushing are listed among the mechanical causes of internal cell damage that may not show external symptoms right away. A battery involved in a crash or a hard drop warrants a check with the manufacturer before its next charge, even without visible deformation.
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