Eleaf iStick 40W TC Box MOD Grey

Overview

The Eleaf iStick 40W TC Box MOD Grey by Eleaf in Grey at 0mg. Free UK delivery over £20, same-day dispatch on weekday orders before 4pm.

Eleaf iStick 40W TC Box MOD at a glance

The Eleaf iStick 40W TC Box MOD is a compact, rechargeable box mod from Eleaf, a manufacturer with a long record in the refillable vaping market. It is not a sealed, throwaway device. Instead it is a battery-and-chip platform that you pair with a tank or atomiser of your choice, then fill with e-liquid in the strength and flavour you prefer. That makes it a very different proposition from the single-use vapes that used to dominate UK shop counters, and it is the reason this style of device still appeals to people who would rather own one reliable piece of kit than keep buying replacements.

The headline specification is straightforward. You get a built-in 2600mAh battery, variable wattage output up to 40W, a temperature control mode for compatible coil wires, a standard 510 connection, micro USB charging and a small OLED screen that shows wattage, resistance, battery level and puff information. The firmware can be updated through the USB port, which is useful if Eleaf releases a refinement after you buy.

• Output range: variable wattage up to 40W
• Battery: built-in 2600mAh lithium-ion, charged by micro USB
• Modes: variable wattage, plus temperature control for nickel, titanium and stainless steel coils
• Connection: 510 thread for standard atomisers
• Screen: compact OLED with a three-button layout

This listing has 8 variants in the same family. They share the same electronics, so the choice between them is a matter of finish and colour rather than performance. Depending on the variant and listing you choose, the mod may arrive on its own or alongside an atomiser, so check the contents list on the product page before ordering if you need a tank straight away.

In the sections below we cover what the iStick 40W actually delivers day to day: power, temperature control, flavour, build quality, battery life, coil choices, nicotine strength, who it suits, how to use it, how to fix common faults, and how it compares with the alternatives. We have tried to be straight about its limits as well as its strengths, because a 40W mod with a fixed battery is a good fit for some vapers and the wrong tool for others.

Power output and day-to-day performance

A 40W ceiling sounds modest next to the 100W-plus mods you will see in online reviews, but it covers the range that most people really use. Variable wattage mode lets you set the output in small increments, and the chip regulates the voltage so the coil receives a steady amount of power as the battery drains. In practice that means the first puff on a full charge and the last puff before you plug in feel broadly similar, rather than fading as an unregulated device would.

The mod is designed for coils from roughly the sub-ohm range up to a couple of ohms in standard wattage mode. In temperature control mode the supported resistance window is narrower, approximately 0.05 to 1.0 ohm, so it is worth checking the manual that comes in the box for the exact figures before you fit an unusual coil.

As a starting point, these wattage ranges are a sensible guide, but always follow the range printed on the coil head, because that is what the manufacturer has tested:

• 1.0 to 1.8 ohm coils (mouth-to-lung): typically 10W to 20W, giving a tight draw closer to a cigarette
• 0.5 to 1.0 ohm coils: typically 18W to 30W for a looser, warmer vape
• 0.2 to 0.5 ohm sub-ohm coils: typically 25W to 40W for a more open, direct-to-lung draw

Response from the fire button is quick and there is no noticeable ramp-up delay once the coil is primed. The chip also provides the usual protections, such as short-circuit detection, low-resistance warnings, over-time cut-off and low-battery protection, so a poor coil fit shows an error message instead of firing unsafely.

The honest limit is power headroom. If your favourite coils call for 60W to 80W, the iStick 40W will not drive them properly, and you will get a lukewarm, underpowered vape. This mod is at its best with coils rated for 40W or below, which includes the great majority of starter-tank coils and many popular mesh heads. It is also worth remembering that higher wattage drains a 2600mAh battery faster, so running at the very top of the range will cost you battery life, a point we cover in more detail further down.

Temperature control mode explained

The TC in the product name stands for temperature control, and it is the feature that sets this mod apart from a plain variable wattage box. Temperature control works by monitoring how the electrical resistance of certain metals changes as they heat up. Nickel (Ni200), titanium and stainless steel (commonly 316L) all change resistance in a predictable way, so the chip can calculate the coil temperature and reduce power when it reaches the limit you set. The iStick 40W supports those three materials and also offers a TCR setting so you can enter a custom resistance coefficient for other wire types. The temperature window runs from roughly 100 to 315 degrees Celsius, or 200 to 600 degrees Fahrenheit.

The practical benefits are consistency and protection. Because the mod caps the coil temperature, dry hits are less likely if your wick starts to run low, and the flavour tends to stay steadier through a tank because the coil is never pushed into a scorched state. Some vapers also find that a temperature-limited vape feels smoother on the throat at a given setting.

There are a few rules you need to follow to make it work:

• Use only TC-compatible wire. Standard kanthal coils do not change resistance in a useful way. If you fire a kanthal coil in TC mode you will get erratic results and possibly a harsh vape, so stay in variable wattage mode for those.
• Set the cold resistance properly. Let the coil cool to room temperature, then lock or set the resistance so the chip has a correct baseline. A coil that is still warm will produce a wrong reading and the temperature calculation will be off.
• Start low. Begin around 200 degrees Celsius and raise it until the flavour and vapour are right.

To be fair, the majority of people who buy this mod never touch temperature control, because the coil heads supplied with most starter tanks are kanthal. If you are happy with ready-made coils, treat TC as a bonus rather than a reason to buy. If you enjoy experimenting with nickel or titanium builds, or buying TC-rated replacement heads where available, it is a genuinely useful tool at this price point.

Flavour and vapour delivery

A mod does not produce flavour on its own. What you taste is the result of the e-liquid, the coil, the airflow and the power setting working together. What the iStick 40W contributes is clean, regulated power, and that matters more than it sounds. A device that delivers a steady wattage lets the coil reach its working temperature quickly and hold it, which is the foundation of a consistent flavour from the first puff to the last.

With a mid-range tank and a coil running inside its recommended wattage window, you can expect a rounded, moderate vapour output. At 40W with a suitable sub-ohm coil there is enough vapour for most people who want a reasonably warm, dense hit without the blast of a high-powered mod. At 12W to 20W with a higher-resistance coil, the flavour is more concentrated and the draw is tighter, which suits mouth-to-lung vaping and those switching from cigarettes or pod devices.

A few simple habits make a noticeable difference to flavour:

• Prime the coil. Put a few drops of e-liquid directly onto the cotton before you fill the tank, then wait five to ten minutes after filling so the wick can saturate fully.
• Match the liquid to the coil. Higher-resistance coils work best with 50/50 PG/VG blends, which wick well and carry flavour strongly. Low-resistance sub-ohm coils prefer thicker 70VG blends.
• Do not chain vape at full power. Give the wick a few seconds between puffs so it can refill, particularly with thick liquids.
• Replace coils on time. A burnt or tired coil flattens flavour regardless of the mod, and swapping it out is the cheapest way to restore taste.

If you are moving over from a disposable, expect more control over flavour than you are used to. You can choose from the whole range of bottled e-liquids, from tobacco and menthol to fruit, dessert and drinks profiles, and change flavour whenever you like by rinsing the tank and refilling. Because the nicotine-containing bottles sold in the UK are capped at 10ml, trying a few flavours without a big outlay is easy.

Design, build quality and handling

The iStick 40W uses a compact box format that sits comfortably in the palm and slides into a jacket or jeans pocket without drawing attention. The body is a metal construction with a coated finish, which gives it a solid, slightly heavier feel than plastic-bodied pod kits. The weight is not excessive, but it is noticeable compared with a slim pod device, and most users find it reassuring in the hand rather than a drawback.

Controls follow the familiar Eleaf three-button layout: a fire button on the front and two smaller adjustment buttons for raising and lowering the setting. The OLED screen sits just above the fire button and is clear enough to read in indoor light and in most outdoor conditions. It shows the wattage or temperature, the coil resistance and a battery indicator, and the interface is simple enough that you can learn it in a few minutes without reading the manual.

• Finish options: the 8 variants in this family are different colourways and finishes on the same chassis
• Atomiser fit: the 510 connection suits standard tanks, and atomisers around 22mm in diameter sit flush with the body
• Ventilation: small vent holes in the casing allow gas to escape safely if the battery ever develops a fault
• Charging port: micro USB, placed on the body for easy plugging in

On build quality, the usual caveats apply to any coated metal device. Keys, coins and other hard objects in a pocket will eventually scuff the finish, and the paint at the edges is where wear shows first. A simple silicone sleeve, if you can find one that fits, protects the finish and improves grip. The buttons have a firm, positive click, and the 510 connection holds an atomiser securely when it is screwed down finger-tight.

It is worth keeping the 510 connector and the area around it clean. A small amount of e-liquid residue can interrupt the electrical contact, and wiping the connector with a dry cotton bud now and then keeps the mod reading the coil correctly. Treat the device gently, avoid dropping it, and keep it out of damp places and direct heat to protect the internal battery.

Battery life and charging

The iStick 40W has a built-in 2600mAh lithium-ion battery. Built-in means it is not designed to be swapped by the user, so there are no loose cells to buy, charge separately or carry. The trade-off is that when the battery is flat you need to plug the mod in rather than slot in a spare, so it is worth topping up when you are near a charger.

We can reason about real-world endurance from the numbers. A 2600mAh cell at around 3.7 volts holds roughly 9.6 watt-hours of energy. After losses in the chip and the connection, a usable figure is closer to 8 watt-hours. At 20W, that is about 24 minutes of actual firing time, which at a typical three-second puff is somewhere around 450 puffs. At 30W the figure falls to roughly 300 puffs, and at the 40W ceiling to about 220. Your results will vary with puff length, coil resistance and how often you vape, but the pattern is clear: lower wattage and higher-resistance coils stretch a charge across a full day, while sub-ohm vaping at higher power will need a top-up by evening.

• Charging: micro USB, and a quality 5V wall adapter delivering around 1A will fill an empty battery in roughly two to three hours
• Pass-through: you can vape while charging, but it is better to let the battery charge undisturbed for the sake of longevity and tidiness
• Cables and chargers: use a reputable cable and adapter, and avoid damaged or unbranded leads
• Unattended charging: do not leave any lithium device charging overnight on soft furnishings or unattended

To look after the battery, try not to run it to zero repeatedly, avoid leaving it in a hot car or in direct sunlight, and store it with some charge if you are putting it away for a while. Like every rechargeable battery, capacity declines gradually over hundreds of cycles, so it is realistic to expect a reduction in daily runtime after a year or two of heavy use.

When the mod eventually reaches the end of its life, do not put it in a household bin. It contains a lithium battery and electronic components that fall under UK waste electrical and battery rules. Take it to a household waste recycling centre, a retailer take-back point or a local WEEE drop-off, and tape over any exposed contacts if the device is damaged.

Atomiser compatibility and coil choices

The 510 connection is the most common thread in vaping, which means the iStick 40W can run a very wide range of tanks, clearomisers and rebuildable atomisers. Most users will pair it with a sub-ohm or mid-resistance tank, and the 22mm size is the sweet spot for a flush, tidy look on this body. Larger atomisers will overhang the edges, which is a cosmetic matter rather than a functional one, though very wide tanks can feel top-heavy on a compact mod.

In the UK, tanks sold at retail are limited to 2ml of capacity, so you will be refilling more often than overseas reviews might suggest. That is a regulatory point rather than a flaw in the mod, and it applies to any tank you buy here. Nicotine e-liquid bottles are likewise capped at 10ml, so the practical rhythm is a small tank topped up regularly from a small bottle.

Your coil choice shapes the character of the vape more than anything else on the device:

• Kanthal or standard prebuilt heads: the simplest option, used in variable wattage mode, with resistances from around 0.5 to 1.5 ohm for most starter tanks
• Mesh coils: larger heating surface for flavour and vapour density, usually in the 0.15 to 0.6 ohm range and suited to the upper half of this mod's output
• Nickel, titanium and stainless steel heads: the choice if you want to use temperature control, where such heads are available for your tank
• Rebuildable atomisers: for experienced vapers who build their own coils, provided the resulting resistance falls inside the mod's supported range

A few safety points apply to all of these. Never fit a coil with a resistance below the mod's stated minimum, make sure the atomiser is screwed on properly so there is good contact, and check that the coil is rated for the wattage you are running. Replace prebuilt coil heads when the flavour dulls, which for many people is every one to two weeks. If you are unsure whether a particular tank is compatible, check its specification for the connection type and recommended wattage range, and compare that with the mod's 40W maximum.

Nicotine strength guidance for the iStick 40W

Choosing a nicotine strength is a separate decision from choosing the mod, but the two are linked, because wattage and coil resistance change how much nicotine you take in with each puff. In the UK, nicotine e-liquid is limited to a maximum of 20mg per ml, which is 2 percent. This cap applies across the market, and the ban on single-use vapes that came into force in June 2025 means refillable devices like this one are now the normal route for most adult vapers.

Here is a practical way to think about it. Higher power and bigger vapour production mean more liquid and more nicotine per puff, so sub-ohm vaping calls for lower strengths. Tighter, lower-power vaping delivers less liquid per puff, so higher strengths are comfortable.

• Sub-ohm coils at 25W to 40W: typically 3mg or 6mg freebase nicotine in a high-VG blend. Using a high-strength liquid at this power is likely to feel harsh and may deliver more nicotine than you intend.
• Mid-range coils at 18W to 30W: typically 6mg to 12mg freebase, or a lower-strength nicotine salt such as 10mg.
• Higher-resistance coils at 10W to 20W (mouth-to-lung): 10mg to 20mg nicotine salt is common, particularly for people moving from heavy smoking or from a 20mg disposable.

If you smoked 20 or more cigarettes a day, a common starting point is 12mg freebase or a 20mg salt with a tighter coil. If you smoked around 10 to 15 a day, 6mg to 12mg is usually enough, and lighter smokers often do well on 3mg. If you find yourself chain vaping or feeling unsatisfied, step the strength up one notch. If you feel light-headed, nauseous or get a harsh throat hit, step it down or lower the wattage.

Nicotine salts and freebase nicotine behave differently. Salts are smoother at high strengths and are best used with higher-resistance coils at modest wattage. Freebase is better suited to sub-ohm devices and gives a throat hit that increases with strength. Please also remember that nicotine is addictive. Vaping is intended for adult smokers and existing nicotine users, not for non-smokers or anyone under 18, and the aim for most people moving over from cigarettes is to reduce strength gradually over time.

Who the iStick 40W is for

The iStick 40W is a straightforward, moderately powered mod, so it fits some people very well and others less so. The quick way to decide is to be honest about how you vape now, and how you would like to vape in six months.

It makes sense for:

• People leaving disposables behind. If you have been buying a new single-use device every few days, a refillable mod is a more sustainable and generally cheaper route, and the iStick 40W is a gentle step up in control.
• Vapers outgrowing a first pod kit. If your pod kit feels limited, this gives you more power, a choice of tanks and coils, and a screen that tells you what is happening.
• Anyone curious about temperature control. At this size and price, it is an accessible way to try nickel or titanium coils.
• Those wanting a compact secondary device. It is small enough to pack for travel or keep in a bag as a back-up.
• Mouth-to-lung and restricted direct-to-lung users. The power range suits the large majority of everyday coils.

It is probably not the right choice for:

• Cloud chasers. If you want 80W-plus output and enormous vapour, you will need a higher-powered device.
• People who want swappable batteries. Because the 2600mAh cell is built in, you cannot carry spares, and heavy daily use may need a mid-day top-up.
• Anyone who wants the simplest possible experience. If you prefer to click in a pre-filled pod and go, a closed pod device is easier, albeit with less choice and usually a higher cost per millilitre of liquid.
• Non-smokers and under-18s. Vaping products are for adult smokers and nicotine users, and it is illegal to sell them to anyone under 18 in the UK.
• Users who need USB-C or app connectivity. This mod uses micro USB and has no Bluetooth features.

If you are unsure, a useful test is to ask whether you would be comfortable filling a tank, charging a device and swapping a coil once or twice a month. If so, the iStick 40W will probably suit you. If that sounds like a chore, a simpler device may be a better fit.

How to use the iStick 40W step by step

Setting up the mod takes only a few minutes. The following steps cover a first-time start-up. The button sequences below follow the common Eleaf pattern, but the manual in the box is the authority for your unit, so check it if anything behaves differently.

• Step 1, charge it. Plug the mod into a wall adapter with the supplied micro USB cable and give it a first full charge before use.
• Step 2, fit the atomiser. Screw the tank on to the 510 thread, finger-tight. Do not use tools or force it, because over-tightening can damage the connector.
• Step 3, prime the coil. Drop a few drops of e-liquid onto the coil head cotton, install the coil in the tank, and fill the tank, keeping the liquid below the airflow holes and out of the central chimney.
• Step 4, wait. Leave it for five to ten minutes so the cotton saturates fully. Skipping this step is the most common cause of a burnt first hit.
• Step 5, switch on. The usual method is five quick clicks of the fire button. The screen will light and display the current setting.
• Step 6, choose your mode. Use variable wattage for standard coils, or switch to temperature control for nickel, titanium or stainless steel coils. In TC mode, set the cold coil resistance first.
• Step 7, set your power. Use the plus and minus buttons to adjust wattage or temperature, starting at the low end of the range printed on the coil.
• Step 8, take a first draw. Press and hold the fire button, inhale slowly and release. Take a few gentle puffs before settling on a setting.
• Step 9, adjust. Increase the setting a watt or two at a time until flavour and warmth are right. If the vape tastes burnt, drop it back down.

For everyday use, keep the mod and tank upright when not in use, and refill before the liquid drops to the bottom of the coil window. Many Eleaf mods offer a key-lock function, usually by pressing the adjustment buttons together, which prevents accidental firing in a pocket or bag. Use it whenever you carry the device.

Clean the connector occasionally, rinse the tank when you change flavour, and let the tank dry before refilling. Carry the mod with the atomiser fitted rather than loose, so the 510 connector stays protected, and keep spare coils in a small pouch so you are never caught out.

Troubleshooting common problems

Most problems with a mod like this come down to a small number of causes, and almost all of them can be fixed at home. Work through the items below in order before assuming the device is faulty.

• The screen shows a no-atomiser or check-atomiser message. Unscrew the tank and screw it back on, making sure it is seated. Wipe the 510 connector and the base of the atomiser with a dry cotton bud. If the message persists, try a different tank to find out whether the coil or the mod is at fault.
• A short-circuit or low-resistance message appears. The coil resistance is below the supported minimum, or the coil head has failed. Replace the coil head and make sure the atomiser is fitted correctly.
• The mod will not fire or does not switch on. Charge it for at least 30 minutes, since a deeply discharged battery can take a while to wake up. Check that the device is not in key-lock mode and try the five-click switch-on sequence again.
• The vape tastes burnt or harsh. The coil is either worn out or was not primed. Replace it, wait for saturation, and start at a lower wattage. In TC mode, check that you are using TC-compatible wire and that you set the resistance when the coil was cold.
• The tank leaks. Most leaks come from the tank, not the mod. Check the coil is screwed in fully, the seals are seated, and the tank is not overfilled. Store it upright.
• Gurgling or spitting. The coil may be flooded, or the liquid may be too thick for the coil. Blow gently through the tank without firing to clear the airway, or lower the VG ratio.
• Battery drains quickly. High wattage and low-resistance coils use more power. Lower the setting, check the cable and charger, and remember that all rechargeable cells lose capacity with age.
• The device gets warm. Mild warmth during charging or heavy use is normal. If it becomes hot to the touch, stop using it, unplug it and let it cool in a safe place. Do not use a mod that is swollen, damaged or leaking.
• It will not charge. Try a different cable and wall adapter, then clean the charging port gently with a dry wooden toothpick or compressed air.

If none of this resolves the problem, contact the shop with your order details and a short description of the fault. A mod that was faulty on arrival is covered by UK consumer rights.

Value for money and how it compares

The iStick 40W belongs in the affordable end of the refillable market, and its value is best judged by cost of ownership rather than the sticker price alone. A rough comparison helps. Before single-use vapes were banned, a regular user might have bought a new device for around five to eight pounds every few days, which can easily pass 50 pounds a month. A refillable mod costs a one-off purchase, then roughly a few pounds for a replacement coil every couple of weeks and a bottle or two of e-liquid. For most people that cuts monthly spending significantly, even allowing for the up-front cost.

How does it stack up against alternatives? Here is a fair comparison:

• Against the Eleaf iStick Pico and similar removable-battery mods: the Pico and its rivals offer more power, up to 75W, and a replaceable 18650 cell, so you can carry spares. The cost is higher once you buy the battery and a charger, and the device is bulkier. The iStick 40W is simpler, lighter and cheaper to get started with, but caps at 40W and has a fixed battery.
• Against modern pod kits: pod devices are easier and often neater in the pocket, but typically offer lower power, little or no temperature control, and in many cases a narrower choice of coils and liquids. A mod gives you more flexibility, while a pod kit gives you more convenience.
• Against other TC mods at a similar price: several brands offer comparable features. The iStick 40W is competitive on compact size and a long record of reliability, while some rivals offer USB-C charging or slightly higher output.

Where it falls short is in the details: micro USB rather than USB-C, a fixed battery, and a power ceiling that rules out the heaviest sub-ohm coils. Those are reasonable compromises at this price, and they do not affect everyday use for most people.

Our overall view is that the iStick 40W is good value for a first mod or a compact second device, particularly if you value a simple interface and the option to try temperature control. If you already know you want high power or swappable batteries, spend more on a bigger device. If you want something dependable that covers the everyday range of coils, this mod does that job without fuss.