Best Battery Cell for Portable Chargers: Comparing 18650, 21700, and Polymer Batteries

Battery cell 18650, 21700, and Polymer Batteries, RAVPower RP-PB201

What do the Tesla Model 3, the newest hoverboards, and fancy vaping mods have in common with your laptop, flashlight, and smartphone? They are all battery-powered and use cordless energy to function.

Things have changed a lot since Sony first popularized the Lithium-ion battery back in 1991.

These days, when you have a quality power bank battery, such as the one in a RAVPower portable charger, you have enough energy to power your favorite devices several times. No cords are necessary; you can charge your devices wherever you are.

You probably have several essential mobile devices— like most people. If you’ve been using a portable charger with an older battery, its charge probably gets depleted very fast. Chances are it runs out of charge when you need it most.

Luckily for you, changes are happening where it matters: in the power bank battery cell. But in order to understand the exciting changes, it’s vital to know the popular power bank battery cells.

We’re also going to tell you what Tesla electric cars and the new RAVPower portable charger 21700 have to do with the changes.    

Let’s get started.

What is An 18,650 Battery?

RAVPower PD power bank RP-PB186 using 21700 battery cell
Model: RP-PB186

It’s a lithium-ion battery cell classified by its size: 18,650. The “18” represents the cell’s 18mm diameter. The “65” stands for its 65mm length, and the “0” denotes the cell’s cylindrical form.

What is a 21,700 Battery?

This is a rechargeable lithium-ion cylindrical cell.

The same naming strategy applies here:

  • 21 represents the 21mm diameter
  • 70 represents the 70mm length
  • 0 represents the cylindrical cell form

What’s the Difference between 18,650 and 21,700 Batteries?

From the measurements above, you can easily tell the new-generation lithium-ion battery cell type 21,700 has a larger volume than the older 18,650 battery cell.

How big of a volume?

Find out the quick volume and energy capacity calculations below. It’s nothing technical, we promise.

What is a Polymer Battery?

RAVPower PD power bank RP-PB201 using 21700 battery cell
Model: RP-PB201

It’s a rechargeable lithium-ion battery cell that uses a polymer electrolyte.

Many polymer batteries available now are Lithium-ion-polymer batteries. The big difference between Li-Ion and Li-Po batteries is the electrolytes used. Li-Po batteries also use a combination of laminated sheets rather than the rigid shells used in Li-Ion batteries.   

Also, while lithium-ion cells adopt the traditional cylindrical and prismatic forms, lithium-polymer cells come in flexible foil pouches.

How Are the Three Battery Cells Different?

We’re comparing five distinct features to help you get a good grasp of the battery cells so you can decide which is the best power bank battery cell for your needs.

Let’s get right to it.

1.     Energy Density

How long do 18,650 batteries hold charge for?

This short calculation below shows that a 21,700 battery offers up to 46% more energy capacity than its 18,650 counterpart.

18650 and 21700 batteries

The 21,700 battery cell achieves that by offering an extra 5mm X 3mm volume and 7,701 cubic millimeters more.


Both the 18,650 and 21,700 batteries are based on the traditional Lithium-ion battery cell. According to research, Li-Ion battery cells have a slightly better energy density compared to Li-Po battery cells. So, if you have many devices to charge, choose a RAVPower power bank with a 21,700 lithium-ion battery cell.

Elon Musk and his team decided to use a variation of the 21,700 Li-Ion battery cells, the Tesla 2170 battery cells, to power the Tesla Model 3 up to 399-499 miles.

That’s a big improvement than what the older two models could achieve on a single charge with their 18,650 Li-Ion battery cells.  

2.     Safety and Stability

This is one of two areas where polymer battery cells outdo Li-Ion cells. High-capacity Li-Ion batteries were in the news a while ago for exploding and were banned from flights in different places.

However, advanced battery technologies by reputable manufacturers have eliminated the issue of Li-Ion batteries exploding if they overcharge or overheat.

For example, despite its incredibly high output, the RAVPower PD Pioneer 20,000mAh 60W portable charger (RP-PB201) comes with an entire safety system (iSmart Technology).

The system is geared towards protecting you, your loved ones, and dear devices from burns, overheating, overcharging, and short-circuiting.

The 21,700 battery technology makes for slower discharging and higher thermal stability than the 18,650 battery technology, according to a 2018 research study

3.     Portability and Weight

RAVPower PD power bank RP-PB186 using 21700 battery cell
Model: RP-PB186

This is another area where the polymer battery cell wins.

While polymer batteries are no longer made of plastic, they still use lightweight, more flexible, and ultra-thin materials that make them suitable for use in highly-portable devices.

That’s why most phones and ultra-thin power banks now feature non-removable Li-Po batteries. The batteries are compact and are usually attached to the devices’ other components.

But we’re not saying that all Li-Ion batteries are huge. Some Li-Ion battery chargers are portable. You don’t have to sacrifice high capacity for portability.

A good example is the RAVPower PD Pioneer 10,000 29W portable charger (RP-PB186). Its battery is made with industry-leading LG 21,700 battery cells. They measure 4.4 X 2.0 X 1.0 inches and only weigh 6.0 oz, making it a great power bank for everyday use.  

4.     Lifespan & Charging Cycles

Li-Ion battery cells tend to have more charging cycles than Li-Po battery cells. How long your Li-Po power bank will serve you depends on the materials the manufacturer used.

The good news is top-tier power bank makers, such as RAVPower, use smart battery technologies, such as iSmart Technology, to detect a device’s optimal charging. The technology helps protect the battery from premature degradation.

5.     Cost

RAVPower PD power bank RP-PB201 using 21700 battery cell
Model: RP-PB201

The gel-based electrolyte and laminated sheets used in Li-Po batteries make them costlier to manufacture than Li-Ion batteries. Li-Ion batteries only have electrolytes, cathodes, anodes, and separators.

Since the cost of production is usually passed on to the end-user, Li-Po devices tend to be more expensive than Li-Ion devices with similar specifications. The higher energy capacity of the 21,700 Li-Ion battery helps reduce battery cell costs by up to 30%. What’s more, the battery has the same output as an 18,650 battery.

That’s how Tesla has managed to sell the Model 3 for a remarkable $35,000. Li-Ion battery chargers also offer the same savings.

More advanced RAVPower portable chargers—such as the RP-PB203—are reasonably-priced and offer bigger benefits.

When you get that RAVPower power bank, here’s how you can ensure it serves you for a long time.

  • Always keep it in a place that’s neither cold or hot
  • When storing your Li-Ion power bank, ensure the battery capacity is 50%
  • Apply the “20-80” rule: always charge your power bank when it discharges to 20% and disconnect it from the wall socket when it charges to 80%
  • Use a power bank battery cell technology that protects your devices’ batteries from decaying 
  • Buy a charger from a reputable brand to protect your loved ones, yourself, and your devices

What Next?

The best power bank battery cell depends on your preferences. If you’re looking for higher power capacity, most Li-Ion power banks will deliver—especially those with newer 21,700 battery cells. Polymer batteries are known for their portability.

A RAVPower portable charger offers the best of both worlds: higher power capacity and portability.   

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