18650 batteries are lithion-ion batteries. Some are rechargeable and others aren't.
This ressource was made to help you find the best 18650 battery for your specific application (This guide focus on rechargeable 18650 batteries).
For your info: The Tesla electric car uses a 18650 rechargeable batteries.Battery Comparison Runtime Estimator
The term 18650 is a reference to the size of the battery. A diamiater and a height of approximatively 18mm and 65mm respectively. 18650 batteries cells have different cells chemistry, and depending on the intended application, one is better than other. (See a lithium-ion battary chemistry guide).
To buy a 18650 battery safely you need to properly distinguish them, understand their labels and then make an informed decison. Below is a easy to digest battery information guide.
Let's compare two popular rechargeable 18650 batteries models to help you understand what to consider when approching batteries.
A battery capacity is determined by the amount of current (A, or Ampere) it can producte over a period of time and mesuared in mAh (milliAmpere-per-hour). This means how much mA (or amount of current) you can draw from a battery in an hour of constant continuous usage. For example, a battery capacity rated at 2500mAh indicate that it can produce 2500mA (or 2.5A) over one hour period. One of the biggest confusion there is with batteries ratings is between energy vs power, but actually power is just energy measured per unit of time in Watts (W). Energy is constant (2500mAh) but power determine how fast you can burn that energy. Battery design allows only for so much energy for the power available, this mean the battery energy the lower capacity.
C in "C Rating" is short for capacity and it is used to calcule the maximum continuous current discharge rate CCDR). The countinous discharge rate is measured in Ampere (A) varies between the types of battery. Depending of the use of the battery you will prefer a higher CCRD (for vaping for example) than a lower CCDR (for electric car). The batteries above show the relationship between power and energy. While the yello LG has a Max CCDR of 20A (compared to 30A of the green LG), it has greater capacity of 2500mAh compare to the only 1500mAh from the green LG(66% greater capacity). Everything being equal the green LG will drain twice faster under the same condition. (battery drain calculator)
A voltage is define as the difference in electrical potential between two points. Electrons which are negatively charged repel one another in the battery creating a pressure called electrical potential. The voltage of a battery always varies throughout the charging and discharging circle. Meaning when you are charging your battery and when you are using it. One of the main advantage of 18650 batteries is that they have a very constant voltage throughout the charge and specially when needed during the discharge cycle (discharge voltage). This allows for a constant power distribution throughout discharge periods. The nominal voltage for all lithium-ion batteries is usually between 3.2V and 3.8V depending on the cell chemistry (most are 3.6V) . The cut-off voltage is the voltage at which the battery is considered to be fully discharged, so you should stop the discharge at this point. With almost identical voltages, you should use the battery capacities and current discharge rates to guide your decision, which makes it fairly simple afterall
Just like diamonds and graphite are made of the same atoms of carborn, all 18650 batteries are a littium-ion composite but with different chemistry. Use the table below to compare between the different cells chemistry.
Batteries chemistry ultimately must trade-off between energy, power, life cyle and safety.
It's clear that you won't be operating your battery near its thermal runway, the operating tempirature of 18650 batteries are usually between -20 ~ 75℃. Temperature is important for the life of the battery. If you constantly overheat your battery by not respecting the Maximun Continous discharge rate (you can in fact go over the limit) or using very low resistance coil in your vapes, your battery life will be shorter. Having higher resitance coils will lower the amount of heat generated by the coil and will keep the battery cooler. Same goes for running lower than maximun continuous current discharge rate.
This is a question that's thrown arond a lot in the battery world but let's clarify it here. A protected battery has a small electronic circuit integrated into the cell packaging. This makes the cell safer and protects against dangers like overcharge, overdischarge, short-circuit (overcurrent) and temperature. An unprotected battery doesn't have that cicuit intregrated. Unprotected 18650 batteries usually have a safer cell chemistry to compensate. Also, you have companies buying them from manufactures to make their own brand. When wrapping the naked cells for their own brand, some companies like UltraFire add the protective circuit on some models. You should get a battery with just a little more current discharge than you need to ensure low operating temperatures and optimal battery fonctionning. Learn more about protected and unprotected 18650 lithium-ion batteries
As mentioned aboved there is a trade off to make between power and energy. The best 18650 batteries are comming closer to provide both. The best approach is to get battery with the Max. discharge current rate you need, and finding one with the highest capacity in that range. We are not including rewraped battery in this guide for the reason mentionned above.
I have arrange the batteries bellow per Maximun current discharge rate and Capacity. They are high quality and relatively safe (when handle properly).
|Sony||Konion US18650VTC5A||35A||2600mAh||13.5C||Best 18650 battery hands down; Great for vaping; High power, energy and safe NMC cell chemistry.||€5.25|
|Sony||Konion US18650VTC5||30A||2600mAh||11.5C||Good power to energy ratio. NMC cell chemistry and great price.||€4.45|
|Panasonic||CGR18650K||30A||1650mAh||18.2C||Handles high current very less capacity; safer than Li-cobalt (IRC); The Sony is a better choice.
This is a Li-manganese cell chemistry
|LG||ICR18650HD2||25A||2000mAh||12.5C||Same cell chemistry as the Panasonic above, safe battery with good capacity with high current discharge rate||$4.32|
|LG||ICR18650HB2||22A||1500mAh||14.7C||Low capacity but high current. Proven performance and safety.||$3.75|
|LG||INR18650HG2||20A||3000mAh||6.7C||Very high capacity and good current discharge rate. A lot of performace. One of the best battery in this range.||$5.99|
|LG||INR18650HE4||20A||2500mAh||8C||Still great capacity, lower than the HG2, but cheaper. Buy this if the HG2 is not available.||$5.22|
|Samsung SDI||INR18650-25R Green||20A||2500mAh||8C||Same cell chemistry and metrics as the LG HE4. Too expesive but a great 18650 battery nonetheless||€9.39|
|Samsung SDI||INR18650-30Q||15A||3000mAh||5C||Awesome capacity with enough power. Will give you a better runtime than the LG HE2||€7.95|
|Samsung SDI||INR18650-35E||10.5A||3500mAh||3C||Very high capacity but low max current discharge. A great choice when you don't need a lot of power.||€5.45||LG||INR18650MJ1||10A||3500mAh||2.9C||Good alternative for the Samsung ablove, cheaper with the same capacity and good power.||€4.95|
|Learn how to calculate the C rating here here and estimate your battery drain time.|