Everything You Need to Know About the 18650 Battery

By August Neverman

This post tells you everything you need to know about 18650 batteries. We’ll talk about different types, features, charging, lifespans, and our recommendations for batteries and chargers.

What is an 18650?

An 18650 is a lithium ion rechargeable battery. Their proper name is “18650 cell”. The 18650 cell has voltage of 3.7v and has between 1800mAh and 3500mAh (mili-amp-hours).

18650s may have a voltage range between 2.5 volts and 4.2 volts, or a charging voltage of 4.2 volts, but the nominal voltage of a standard 18650 is 3.7 volts.

There are two types; protected and unprotected. We absolutely recommend protected cell 18650 batteries. Protected cells include a protection circuit that stops the cell from being overcharged.

Unprotected cells can be overcharged and burst or potentially cause a fire unless there are specific electronics to protect the battery. The popular LG HG2 and Samsung 25r are both UNPROTECTED batteries, only use them in a device designed to use unprotected 18650s

We also recommend you stick with high quality brand name 18650s. Knock offs may lie about high mAh.

The average 18650 battery charge time is about 4 hours. Charge time can vary with amperage and voltage of the charger and the battery type.

Comparing Common Battery Comparisons

Battery Make and Type	Rechargeable	Voltage	Max Milliamp hours	Watt hours	Length & Diameter
Nitecore 21700 (included for comparison)	YES	3.7v	5000 mAh	18.5	L: 74mm (2.92 in) D: 21.4mm (0.84 in)
Samsung 35E	YES	3.7v	3500 mAh	12.5	L: 65mm (2.55 in) D: 18mm (1. in)
XTAR Li-ion 14500	YES	3.7v	800 mAh	2.9	L: 50 mm (1.96 in) D: 14 mm (0.55 in)
Energizer Lithium AA	NO	1.5v	3000 mAh	4.5	L: 50.5 mm (1.99 in) D: 14.5 mm (0.57 in)
Eneloop Pro AA	YES	1.2v	2550 mAh	3.0
Energizer Lithium AAA	NO	1.5v	1000 mAh	1.5	L: 44.5 mm (1.75 in) D: 10.5 mm (0.41 in)
Eneloop Pro AAA	YES	1.5v	950 mAh	1.4
12v car battery (included for comparison)	YES	12v	40,000 mAh	480

More info on the 21700: Everything You Need to Know About the 21700 Battery

Various Battery Sizes

Comparing sizes in the picture above the 18650 is 1170 cubic mm, the 14500 and AA are 700 cubic mm, the AAA is 467 cubic mm. Note the 14500’s cannot be used in all AA devices unless they support both 3.7 and 1.5 volt batteries. The 21700 at 1550 cubic mm, is larger than the 18650 battery – the 21700 and 18650 is not interchangeable.

Protected vs Unprotected 18650 Batteries?

18650 protected batteries have an electronic circuit. The circuit is embedded in the cell packaging (battery casing) that protects the cell from “over charge”, heat or “over discharge”, over current and short circuit. A 18650 protected battery is safer than an 18650 unprotected battery (less likely to overheat, burst or start on fire).

Unprotected 18650 batteries are cheaper, but we do not recommend their use. Unprotected batteries should only be used where the load/draw and charging is externally monitored and controlled. The protected batteries normally have a “button top”, but check the specifications to make sure. Generally 18650 flat top batteries do not include the protection circuit.

If a battery is damaged or looks corroded or appears to be leaking, get rid of it at a battery recycling center. Be safe.

See “Battery Recycling – How to Recycle Different Battery Types and Corroded Batteries Safely“.

How much power does an 18650 have?

A 3.7v a 3400mAh 18650 stores about 2 aH to max of 3.5 aH. It can store about 10 to 13 watt hours. A small air conditioning unit that can cool about 9000 BTU uses about 1100 watts per hour. So it would take more than 110 of the 18650 batteries to run the air conditioner for 1 hour.

In comparison you would need three 12v 40 amp car batteries. But 110 18650s are smaller than three car batteries.

How many times can you recharge an 18650 or other battery?

Recharge cycles vary and are limited. Think of it like a bucket. The trick is that the bucket also gets filled with other junk over time, so there is less room. As the battery is reused (recharged), the battery degrades due to oxidation and electro-chemical degradation.

This happens to any rechargeable battery such as an 18650, 21700, 26650, 14500, AA, AAA or even a car battery. They can only be recharged a limited number of times.

You want to select rechargeable batteries that can be recharged many times. We specifically recommend 18650’s because they have the ability to be recharged 300 to as many as 2000 times.

How frequently should I recharge my 18650?

The way you recharge your battery impacts the life of the battery. If you can measure it, you want to deplete from 3.7v down it to about 3v before you recharge. If you are not sure, use the device until it indicates a battery needs to be replaced. For a flashlight, run it till the light is dim or goes out.

A good charger will tell you the voltage of the battery so you can eventually get a sense of the life of the battery in various devices. If you recharge too frequently you “use up” the life without a return.

Some people don’t let it dip below 3.3v (or even higher). Each brand and model of 18650 has different maximum cycles. So this is really a process of matching your device and usage to the life cycle of the battery.

Be aware that an 18650 battery that drops below 2.5v may “lock” the device so it can’t be used. The “lock” function happens in devices such as vaping devices.

How do I know my 18650 is Dying?

Here is a list of 7 ways you can tell if you need to get rid of an 18650 (or other rechargeable battery). Look through these to determine if your 18560 is nearing the end of its life and needs to be retired:

1. The battery will lose a charge on the shelf must faster than normal. It loses it’s charge after a couple of days or even worse overnight.
2. The battery gets hot when charging or discharging, warmer than normal.
3. You have used the battery frequently over 2 to 3 years.
4. The battery can hold less than 80% of its original capacity.
5. Recharge time gets abnormally long.
6. If there is ANY cracking or deformation in the battery.

These are the 6 signs your 18650 is dead and it is time to get a new one. If you ignore these warning signs you risk fire or even having the battery explode while being recharged.

How can I measure the quality of an 18650 if I am unsure of the age of a battery?

A trick is to buy one or two similar 18650s and mark them “new” with a Sharpe (or label them A, B, C, etc). Then use them and compare their voltage and discharge rates with the questionable 18650s.

Basically you are comparing good vs unknown this way.

You can also gauge temperature this way. Charge both the new and unknown one to see how hot the new one is compared to the one you are unsure of.

18650 Battery Chemistry

There are a number of different chemical combinations for 18650 batteries. We recommend that you focus on protected mode, the chemistry can change and isn’t always reported. Many simply say Li-ION (meaning Lithium Ion). There are actually a number of Li-Ion batteries. Here are some of the current “types”. Depending on your device type one might be better than the others.

1. LiFePO4 which is Lithium iron phosphate
   • also known as IFR or LFP or Li-phosphate
2. LiMn2O4 which is Lithium manganese oxide
   • also known as IMR or LMO or Li-manganese (high amp draw)
3. LiNiMnCoO2 which is Lithium manganese nickel
   • also known as INR or NMC (high amp draw)
4. LiNiCoAlO2 which is Lithium nickel cobalt aluminum oxide
   • also known as NCA or Li-aluminum
5. LiNiCoO2 which is Lithium nickel cobalt oxide
   • also known as NCO
6. LiCoO2 which is Lithium cobalt oxide
   • also known as ICR LCO Li-cobalt

18650 Features

A battery might say protected mode 3.7v 18650 3000 mAh low self discharge. What does that all mean?

• “protected mode” as noted above means it has an overcharge and overdraw circuit protection built in.
• “3.7v” – is the optimal or peak voltage. It will drop as you use the battery.
• “3000 mAh” measures the amp hours the battery can provide. A higher number is better. The highest realistically availble on an 18650 today is about 4000 mAh, anything higher than that is marketing hype.
• “Low self discharge” is a good thing. That means it will hold a charge in storage. The less it loses in storage the more charge will be left for you to run your flashlight or other device.

What are 18650 batteries used for?

Flashlights, electronics, laptops, vaping and even some electric vehicles use 18650s. The Tesla uses 7180 of these batteries. Many high lumen flashlights such as the Thrunite TN14 or Fenix PD35 use the 18650 or the even larger 21700.

Laptops and other electronic devices use one or more 18650’s and have recharging electronics built in. 18650’s are also used in vaping (smoking) devices.

18650s are are generally Lithium Ion batteries. If you are familiar with electronics you can change out some battery packs manually, but be careful – using the wrong type of 18650 or using it incorrectly can cause a fire.

Which is the Best 18650 Battery?

Overall best 18650 battery – The Orbtronic 18650 battery. This is an 18650 3.7v 3500mAh Protected cell. This is a high drain battery. We like it but it is expensive.

Best low cost 18650 battery – The LG18650b. The Panasonic 18650 is an 18650 3.7v 3400mAh Protected cell. Less expensive and slightly lower amp hours. This cheap 18650 battery is still more expensive than the unprotected ones.

Note: Some resellers don’t clarify if the NCR is protected or not – buyer beware.

What is the best travel 18650 battery?

Nitecore NL1834R (currently not available on Amazon but available directly from Nitecore). This is an 18650 3.7v 3400mAh protected cells with a built-in micro-USB charger. It is a few dollars more, but it allows you to charge it on the go and not have to carry a dedicated charger. The unit we have has slightly different packaging.

What 18650 Brands are Best?

The Orbtronic, Samsung, LG, Panasonic and Nitecore are good reliable 18650 rechargeable cells. Be sure to buy them from a reputable source such as Amazon, Top18650battery or direct from the manufacturer.

We don’t use the lower voltage and amperage 18650s, because they have lower amp hours and low peak wattage and lower sustained wattage.

We are willing to pay a few more dollars for the longer life, higher capacity and better quality.

18650 Battery Charger

18650 batteries are rechargeable, so you will need a good charger. We use two different 18650 chargers.

The best 18650 battery charger is the Nitecore i4 because it can charge pretty much anything.

Specifically, it supports: lithium ion 26650, 22650, 21700, 18650, 17670, 18490, 17500, 18350, 16340 (the 16340 is also known as RCR123), 14500, 10440 and Ni-MH and Ni-Cd AA, AAA, AAAA, C rechargeable batteries. This is our favorite charger for the 18650s.

Our runner up is the XTAR VC4 Charger. It is a USB powered 18650 charger. It charges the batteries with any USB power source. This unit is dependent on the power source.

It has an LCD display for charging status. A 2amp interface yields slower charge speeds. Even the 5amp is slow because it charges at .5 amps. We have used the XTAR with a Nektek solar panel that has a 2amp USB interface and it has consistently worked.

18650 Flashlight

The best 18650 flashlight is the Fenix PD35. It is not cheap but it is durable and very bright, and has a pocket clip. The light level is 1000 lumens, and it is water resistant to IPX8.

It has six modes 1000 Lumen Turbo; 500 Lumen High; 200 Lumen Mid; 60 Lumen Low, 8 Lumen Eco and the 1000 Lumen strobe. Firemen, law enforcement and military personnel regularly use this tactical flashlight.

The best mid to low priced 18650 flashlight is the Thrunite TN12 1050 lumen flashlight. It is about 1/2 the price of the PD35 and slightly brighter. It is a GREAT buy (we have a couple in emergency kits).

Either of these are great LED Flashlights that use the powerful 18650 battery.