What CDR means on a vape battery, and how to check yours is enough

Every lithium cell can only push so much current before it gets uncomfortably hot inside. The continuous discharge rating is the highest current, in amps, it can deliver steadily while staying within its safe temperature range.

Wraps sometimes print a bigger pulse or peak figure too. That is how much the cell can manage in short bursts, and it is the number marketing loves. For vaping, where you might hold the fire button for several seconds, the continuous figure is the one that counts.

Genuine vape-grade 18650s typically sit somewhere between 15A and 25A continuous, with higher-capacity cells at the lower end. If a wrap claims both huge capacity and huge amps, be suspicious.

In a regulated mod, the chip delivers the wattage you set whatever the battery voltage, so the current drawn from the battery rises as the cell drains. The formula is simple: amps = watts divided by battery voltage.

Use 3.2V rather than the full 4.2V, because that is close to where a cell sits under load near the bottom of its charge, which is the worst case. The mod's circuit also loses a little energy as heat, so the true figure runs slightly higher again.

At 80W on a single cell that works out at 25A, which is already at or beyond the rating of most genuine 18650s. That is exactly why higher-power mods tend to use two cells, or a 21700.

Mechanical mods and some simple unregulated devices send the battery's voltage straight to the coil. There is no chip deciding the power, so the coil's resistance sets the current: amps = volts divided by ohms.

A fresh cell at 4.2V on a 0.15 ohm coil pulls 28A. Drop to a 0.3 ohm coil and it halves to 14A. Lower resistance always means more current, which is why sub-ohm builds on unregulated devices need careful maths every single time.

Plug your voltage and coil resistance into the calculator below and compare the amps against your cell's continuous rating. If the answer is close to or above the rating, raise the resistance or change the cell.

Most dual-battery mods wire their cells in series, which stacks the voltages. Two cells at 3.2V each give the chip 6.4V to work with, so at the same wattage each cell supplies half the current a single cell would.

That is why a dual 18650 mod can run 160W with the same current per cell as a single 18650 at 80W: 25A either way. Push to 200W and each cell is being asked for around 31A, which is beyond most 18650 ratings.

Series wiring has a catch: both cells carry the same current, so a weaker cell gets worked harder. That is why matched pairs matter so much.

A cell run right at its continuous rating heats up, its voltage sags harder under load and it loses capacity faster over its life. Run the same cell at half its rating and it stays cooler, gives a steadier hit and lasts more charge cycles.

A practical rule: pick cells whose continuous rating sits comfortably above the current your calculation gives, not just level with it. If the numbers are tight, either lower the wattage, move to a 21700 or move to a dual-cell mod.

Buy cells from an established UK vape shop, from the 18650 range or the wider batteries section, and check the rating against the maker's own datasheet.

Capacity and current trade off against each other inside a given cell size. A genuine 18650 rated for high current gives up some capacity to get there, and vice versa. So a wrap claiming 3500mAh and 40A continuous is claiming something the big cell makers do not sell.

Inflated ratings usually come from rewrapped cells sold under made-up brand names. The cell inside might be decent, but its true rating is lower than the sticker says, which defeats the point of doing the maths at all.

Our guide to reading a battery wrap shows what genuine markings look like. Then test yourself below.