Choosing An 18650 Battery
Brand / Manufacturer
The first thing to consider when choosing an 18650 battery for your device or project is the battery brand. Not all brands are created equal and often times you will find are not very truthful in their battery ratings. This is especially true when discussing the Chinese re-wrapping brands. The goal of any manufacturer or brand is to sell as many batteries as possible but some companies have been known to exaggerate their ratings to appear to offer a better product than the other. This practice of exaggerating battery specs is unlawful and can be very dangerous to consumers if gone unchecked. Thankfully, there is a watchdog in the lithium ion battery industry known as the battery mooch who provides thorough testing and will call out these companies for their unlawful practice.
There are five major brands that manufacturer batteries who you can rely on to provide quality, consistent and truthfully rated batteries and those brands are; LG Chem, Molicel, Samsung, Sony|Murata and Panasonic|Sanyo. These brands are well established and have long standing tradition, values and standard to uphold. Any manufacturer specs provided by these brands is well documented and tested many times over. You will often see the battery outperform the manufacturer ratings put forward from these brands.
Other brands such as Efest, Vapcell, Imren and MXJO have been established for a few years and their quality has certainly improved. These brands tend to slightly exaggerate the battery ratings for their products in an effort to appeal to the consumer and sell more. It should be noted these companies do not actually produce their own lithium ion battery but instead purchase them from other manufacturers and then wrap the battery and add packaging to make the battery suitable for retail sale. They do often provide value by using a thicker PVC wrap on the battery which provides an extra layer of protection. As well these brands often include a battery carrying case with all of their batteries.
There are various other unknown brands with all sorts of unrealistic ratings. As of 2021, there is not a single 18650 lithium ion battery rated above 3600mAh capacity or a 30A CDR. If you see any 18650 battery marketed above these specs, you should be very weary of what you are actually getting as it is absolutely certain to be false and exaggerated.
Given the choice, everyone would choose a battery with the highest capacity. Capacity is measured in milliampere-hours (mAh) and this tells us how many milliamps we can draw from the battery for how many hours. However, capacity comes at the cost of current rating (CDR). Inside of each cell, they can only fit so much material so you often have to choose between a high capacity battery OR a high current battery. Take for example the LG HB6 which has a CDR of 30A but only a capacity of 1500mAh. On the other end of the spectrum is the Panasonic NCR18650B which has a CDR of only 4.9A and capacity of 3400mAh.
There are some batteries that manage to balance capacity and current rating such as the Samsung 25R, LG HG2, and Samsung 30Q. All three of these batteries provide a great balance of capacity and current.
Continuous Discharge Rating (CDR)
This is probably the most important thing to consider when selecting a battery. You need to know how much current the device you are trying to power requires before choosing your battery. If you choose a battery with a current rating less than what you need, you will notice the battery overheating as it is working beyond its ability to keep up. There are also two terms you should know that are discussed in battery current ratings. Those terms are continuous discharge rating (CDR) and the pulse discharge rating (Pulse).
CDR – The maximum current at which the battery can be discharged continuously and safely per manufacturer testing without damaging the battery. Pushing a battery to limits beyond it's ability will greatly increase the risk for battery failure.
Pulse Rating - The maximum current at which the battery can be discharged for a short period of time without damaging the battery or reducing its capacity.
We avoid using any pulse ratings as there are far too many factors to consider when pulsing a battery such as pulse length, time at rest between pulses and battery temperature to accurately compare two batteries. For these reasons, we use the CDR rating which is the current rating at which the battery can be continuously discharged at safely without overheating or damaging the cell.
When someone refers to a battery “hitting harder”, what they are referring to is the voltage at which a battery can sustain midway through its cycle, commonly referred to as voltage sag. Some batteries can remain around 3.7V midway through the cycle while other batteries will drop to 3.2V or lower when drawing power causing a sag in power.
Operating Temperature – If your battery is consistently reaching a high temperature and getting hot, this is a warning sign that the battery is being pushed too hard. A battery that is consistently rising above 45C will certainly age faster than a cool running battery. They can also be dangerous as the potential for venting and/or bursting is increased greatly with a high temperature lithium ion battery. You should consider choosing a battery with a higher CDR rating.
Flat top and Button Top – One final thing you want to consider is whether you need a flat top battery or a button top battery. This is referring to the positive end of the battery. A button top battery has a protruding surface which increases the battery’s length and may not fit in a device which requires a flat top battery. A flat top is as the name suggests a flat surface and may appear to be too short if your device is requiring a button top battery.