Lithium-ion battery: safety and choice for e-cigarettes

A lithium-ion battery is a rechargeable cell in which lithium ions move between two electrodes during charging and discharging. In practice, this means: high energy density, relatively low weight and many charge cycles – typically 300 to 500 full cycles before the capacity noticeably decreases.

In the vaping sector, you’ll mainly come across three cell types:

• 18650 – 18 mm diameter, 65 mm length. The classic choice for single and dual-battery mods.
• 21700 – larger, higher capacity (usually 3000–5000 mAh), ideal for high-performance sub-ohm setups.
• Integrated cells – permanently fitted in pods or disposable devices, non-replaceable.

Nominal voltage is 3.7 V, fully charged at 4.2 V, deeply discharged below 2.5 V. It is important to distinguish between capacity (mAh, i.e. runtime) and current capacity (A, the so-called CDR or continuous current value). For sub-ohm coils, the ampere value often matters more than pure capacity.

The battery supplies power to the coil, which heats and vaporises the e-liquid. The lower the resistance of the coil, the higher the current flowing from the cell. For example: with a 0.15-ohm coil and a voltage of 4.0 V, around 27 A flows – the cell and the mod must be able to withstand this continuously.

Regulated vs. mechanical mods

In regulated mods, a chipset sits between the battery and the coil. It monitors voltage, temperature and short circuits. This is the clearly recommended option for beginners.

In mechanical mods, the current flows unfiltered from the cell to the coil. They are not suitable without a sound understanding of Ohm’s law, cell chemistry and battery safety.

Pod systems and disposable devices

Here, the battery is permanently built-in and can be charged via USB-C. Capacities between 400 and 1500 mAh are common. Advantage: no handling errors with loose cells. Disadvantage: if there is a fault, the whole device is affected.

Vape battery safety starts at the point of purchase. Cheap, no-name cells from unclear sources are the main risk for incidents. Pay attention to the following points:

• Genuine products from well-known manufacturers – Sony/Murata, Samsung, LG, Molicell. Counterfeits are circulating, particularly with 18650 cells featuring unrealistically high mAh ratings (over 3500 mAh is hardly possible from reputable sources).
• Suitable CDR value – choose a continuous current rating at least 20% higher than your actual requirements. Pulse ratings are marketing claims, not operating points.
• Undamaged wrap – the plastic casing must be intact. A torn wrap poses a short-circuit risk and must be replaced immediately (special wrap sets are available at low cost).
• Same age for dual setups – always buy two cells for a mod as a pair, and charge and discharge them together. Never combine an old one with a new one.
• Transport in a battery case – never carry loose cells in your trouser pocket or handbag with keys and coins. A small silicone or plastic case is sufficient.

Common mistakes include overcharging with cheap chargers, charging at temperatures below 0 °C or above 45 °C, and ignoring minor mechanical damage. An external charger with individual cell monitoring is preferable to any USB charging port in the mod if you want to use the cells long-term.

How long does an 18650 battery last?

With daily use, typically 6 to 12 months. If the runtime per charge drops significantly or the cell becomes warm, it’s time for a replacement – regardless of the calendar.

Can I take lithium-ion batteries on a plane?

In hand luggage, yes; in checked-in luggage, no. Loose cells must be transported in a protective case. Airlines have their own specific rules, so it’s worth checking the regulations before your flight.

What should I do with faulty batteries?

Do not put them in the household waste. In Switzerland, every retailer takes back old cells free of charge (INOBAT system). Until you hand them in, insulate the terminals with adhesive tape and store them in a dry place.

Can a lithium-ion battery explode?

Very rarely, if used correctly. Thermal runaway is usually caused by a short circuit, mechanical damage or severe overcharging. Genuine cells, a battery box and a regulated mod reduce the risk to practically zero.

A lithium-ion battery is not a standard consumable, but the most safety-critical component of your e-cigarette. If you use original cells, match the CDR value to your own setup and transport cells separately, you have the majority of risks under control. In our selection of chargers and battery accessories, you’ll find suitable boxes and chargers, and if you’re planning a new mod, it’s worth taking a look at the battery mod category for a solid foundation.