NiCd, NiMH, and Lithium Rechargeable AA Batteries

AA batteries are some of the most popular battery types commonly used in a broad range of devices, tools, toys, and other applications.

While non-rechargeable AA batteries feature nominal voltage of more or less constant 1.5 volts, rechargeable AA batteries feature nominal voltage of 1.2 to 3.7 volts, and are offered in a large number of chemistries, raising various questions, among others, which rechargeable AA battery is compatible with non-rechargeable AA batteries?

Published: October 15, 2021.

Fortunately, with the advancements in chemistry and batteries in general, the advancements in electronics lead to more and more devices accepting batteries with different voltages, which is great but should be done only when explicitly allowed by the device's manufacturer.

AA and 14500 Battery Dimensions and Features

AA batteries feature physical dimensions of (D x H) 14.5 x 50.5 mm, while 14500 batteries feature physical dimensions of (D x H) 14.0 x 53.0 mm.

It is important to note that historically, AA batteries were non-rechargeable batteries featuring nominal voltage of 1.5 volts and Zinc-Carbon and Alkaline chemistry, while 14500 batteries were and still are rechargeable lithium batteries featuring 3.2-3.7 volts and various lithium chemistries.

The following comparison table lists some of the most popular AA and 14500 battery chemistries with their most important features and specifications:

As one can see, the most common rechargeable AA battery chemistries include:

- Nickel Cadmium (NiCd) chemistry,

- Nickel Metal-Hydride (NiMH) chemistry,

- Nickel Zinc (NiZn) chemistry,

- Lithium-Ion chemistry (IMR, IFR, ICR, INR).

Note: Lithium 1.5V rechargeable AA batteries feature lithium-ion battery combined with small DC-DC inverter which lowers output voltage from 3+ volts down to very constant 1.5 volts, making such batteries backward compatible with older 1.5V Carbon-Zinc and Alkaline batteries. But, more on that later in this article.

Also, all rechargeable batteries should be recharged with battery chargers intended for such battery chemistry. Using the wrong battery charger may cause the battery to overheat, catch fire or even explode. Seriously!

Nickel Cadmium (NiCd) Rechargeable AA Batteries

Nickel Cadmium (NiCd) rechargeable AA batteries are an older type of rechargeable batteries, slowly being phased out due to the use of toxic cadmium.

NiCd AA batteries feature a nominal voltage of 1.2 volts and an average capacity of 600-1000 mAh. Also, they suffer from strong memory effect - it is highly recommended to periodically discharge them completely and then to recharge them completely.

NiCd AA batteries are still used in various toys and tools that require strong currents.

Also, NiCd AA batteries can replace 1.5V non-rechargeable AA batteries in toys and devices that tolerate somewhat smaller voltage - after all, a cutoff voltage of Zinc-Carbon and Alkaline batteries is lower than the nominal voltage of NiCd AA batteries.

In most applications, 1.2V NiCd batteries are replaced by environment-friendly 1.2V NiMH batteries, but they are still, nonetheless, used in some toys and cordless tools.

Nickel Metal-Hydride (NiMH) Rechargeable AA Batteries

Nickel Metal-Hydride (NiMH) rechargeable AA batteries feature a nominal voltage of 1.2V and capacity in a rather broad range of 700-2800+ mAh.

The main reason for a broad capacity range is that some NiMH batteries are optimized for high-discharge applications and some for high-capacity but low discharge current applications.

NiMH AA batteries are environment-friendly batteries since they don't contain mercury, cadmium, lead, and other toxic and dangerous pollutants. Nonetheless, they should be recycled properly.

NiMH batteries support more charging/discharging cycles than NiCd batteries and they generally don't suffer from memory effect, at least not as much as NiCd batteries.

Also, new NiMH batteries feature a very low self-discharge rate, allowing them to be stored for up to a year without adverse effects on their performances.

Thanks to general compatibility with 1.5V Zinc-Carbon and Alkaline batteries, NiMH batteries are commonly used instead of non-rechargeable AA batteries in toys, tools, medical instruments, photo equipment, etc.

Nickel Zinc (NiZn) Rechargeable AA Batteries

Nickel Zinc (NiZn) AA rechargeable batteries feature nominal voltage of 1.6-1.65 volts and capacity in the 1500-1800 mAh range.

As such, NiZn AA batteries are backward compatible with 1.5V AA batteries, at least in most devices.

NiZn rechargeable AA batteries feature a relatively low self-discharge rate, allowing the users to store these batteries up to 3-4 months without recharging.

Also, photo equipment designed for 1.2V NiMH batteries may have issues or can be even damaged if, for example, four 1.2V NiMH batteries (total 4.8V) are replaced with four 1.6V NiZn batteries (total 6.0-6.2V).

But, the devices that support the use of NiZn batteries will mostly benefit from a switch from 1.2 NiMH to 1.6V NiZn batteries.

Lithium Rechargeable AA/14500 Batteries

The most common rechargeable 14500 lithium batteries are:

- IMR 14500 batteries are based on LiMn₂0₄ (Lithium Manganese Oxide) chemistry, their nominal voltage is 3.6 - 3.7 V, maximum recommended charging voltage is 4.2 V. IMR batteries commonly have a smaller capacity but are capable of delivering stronger currents.

- IFR 14500 batteries are based on LiFePO₄ (Lithium Iron Phosphate) chemistry, their nominal voltage is 3.2 - 3.3 V per cell, maximum recommended charging voltage is 3.5 - 3.6 V.

- ICR 14500 batteries are based on LiCoO2 (Lithium Cobalt Oxide) chemistry, their nominal voltage is 3.6 - 3.7 V, with a maximum recommended charging voltage of 4.2 V. They commonly have higher capacities, but maximum allowed currents are limited to just a few C, if even that.

- INR 14500 batteries are based on LiNiMnCoO2 (Lithium Manganese Nickel) chemistry. Very similar to IMR batteries, they can provide plenty of currents, with slightly lower capacity.

But, there are also other chemistries in use or being developed.

Also, one must note that the physical dimensions of AA batteries are 14.5 x 50.5mm and 14.0 x 53.0mm for 14500 batteries.

Due to the height difference, not all battery compartments intended for AA batteries can accept 14500 batteries.

Note: due to the voltage difference, not all devices can accept both 1.5 volts AA and 3+ volts 14500 batteries.

IFR14500 Batteries - Lithium Iron Phosphate (LiFePO₄) 14500/AA Batteries

IFR14500 lithium batteries, also known as LiFePO4 14500/AA batteries feature a nominal voltage of 3.2 volts and a nominal capacity of 500-750 mAh.

Although IFR14500 batteries feature somewhat lower capacity, voltage, and discharge current than other lithium chemistries, LiFePO4 chemistry is the safest lithium battery chemistry.

IFR14500 batteries are often used in solar rechargeable lights and other low-drain applications where harsh conditions require reliable and safe batteries.

Lithium-Ion 14500/AA Batteries

"Lithium-Ion 14500/AA batteries" is a common label for IMR, INR, and ICR 14500/AA batteries, which feature nominal voltage of 3.6-3.7 volts and capacity in a broad range of 600-2000+ mAh.

Again, some batteries are designed for high-capacity and low-current applications, while other batteries are able to provide strong currents, but feature lower capacity.

Devices that accept both 1.5V and 3.7V batteries can benefit greatly from switching from 1.5V batteries to 3.7V batteries in terms of performance. However, devices that do not support the use of 3.7V batteries can be easily damaged - before switching from 1.5V to 3.7V batteries, be sure to check the Owner's Guide/manual of the device that You have.

To help users with non-compatible devices, some manufacturers provide 1.5V lithium-ion batteries - these are "classic" 3.2-3.7 lithium rechargeable batteries with built-in DC-DC converters which lower batteries' 3.2-3.7 volts to the required 1.5V.

Such batteries often feature a very constant 1.5V output, with the nominal capacity often in 1000-2000+ mAh (@1.5V).

In order to recharge them, the batteries usually feature a USB charging plug, allowing the users to recharge them by simply plugging them into any USB port found on laptops, desktops, or wall chargers.

Some lithium 1.5V AA batteries feature a Type-C USB port, which requires less space than a full-size USB plug, ensuring a larger nominal capacity. Also, by using a splitter charging cable, the user can recharge several batteries using just one USB charging port.

Long Story Short: When compared with non-rechargeable AA batteries, rechargeable AA batteries can save plenty of money in devices that are used regularly, especially on a daily basis.

Before switching from non-rechargeable AA batteries to rechargeable AA batteries, check the documentation of your device and verify what kind of rechargeable AA batteries are allowed/compatible - after all, their voltage can vary from 1.2 volts to 3.7 volts. And that is a huge difference...