Battery Equivalents and Replacements

Nickel Metal Hydride (NiMH) Battery Chemistry

A Nickel Metal Hydride (NiMH) battery is a rechargeable type of battery with a nominal voltage of 1.2V per cell. NiMH batteries use Nickel Oxide Hydroxide (NiOOH) at the positive electrode and hydrogen-absorbing alloy (hydride) at the negative electrode.

When compared with Nickel Cadmium (NiCd) batteries, NiMH batteries feature larger capacity, almost no memory effect, higher energy density, and support a larger number of charging/discharging cycles.

Published: September 9, 2021.

energizer aa nimh

NiMH Battery Features and Specifications

NiMH batteries feature nominal voltage of 1.2 volts, open-circuit voltage up to 1.4 volts, drain voltage under light load up to 1.25 volts, and cutoff voltage down to 1.0-1.1 volts.

Because of this, NiMH batteries are very often used instead of Zinc-Carbon and Alkaline cylindrical batteries, like AAAA, AAA, AA, C-Cell, D-Cell, and similar.

Although Zinc-Carbon and Alkaline batteries feature 1.5V nominal voltage, most devices that accept 1.5V batteries work properly when powered by NiMH 1.2V batteries - Zinc-Carbon and Alkaline batteries feature cutoff voltages below 1.0 volts, lower than the cutoff voltage of the NiMH battery.

Also, NiMH batteries feature very low internal resistance and tolerate high-drain applications much better than Alkaline and especially Zinc-Carbon batteries, making them a preferred battery type (over Zinc-Carbon and/or Alkaline batteries) in high-drain applications.

However, most high-drain applications like flashlights, cameras and similar have switched from NiMH batteries to Lithium batteries.

NiMH batteries support a large number of charging/discharging cycles that vary from a couple of hundreds up to 2000 charging cycles, depending on the battery model, type of charger, battery age, temperature, and similar.

eneloop charger

Older NiMH batteries suffered from memory effect, although much weaker when compared with the memory effect of the NiCd (Nickel Cadmium) batteries. Modern NiMH batteries practically have no memory effect.

However, it is a good practice to periodically fully discharge the NiMH batteries using a battery charger with a discharge function and then recharge it fully again.

Note: discharging the NiMH batteries below a certain level can cause polarity reversal and permanent damage to the battery.

Self-discharge rate depends on the temperature and battery model - for example, Panasonic Eneloop NiMH batteries after 10 years(!) of storage still retain 70% of the initial charge.

Since NiCd batteries contain toxic cadmium, NiMH batteries are preferred batteries for various tools, toys, game controllers, flashlights, electric vehicles, and similar.

However, lightweight lithium batteries are becoming more and more popular and affordable, making them a preferred choice for many applications where lightweight batteries with high energy density are required.

AAAA NiMH Battery

The following chart lists the most common chemistry types of AAAA batteries:

Chemistry Zinc-Carbon Alkaline Nickel-Cadmium Nickel Metal Hydride Lithium-Ion
Rechargeable No No Yes Yes Yes
Typical Voltage 1.5 V 1.5 V 1.2 V 1.2 V ~3.6 V
Typical Capacity 300 mAh 400 - 600 mAh 200-400 mAh 350 - 500 mAh 170 mAh

NiMH AAAA batteries feature a larger capacity than Zinc-Carbon batteries and a capacity very similar to Alkaline AAAA batteries. But, NiMH batteries may be recharged, while Zinc-Carbon and Alkaline AAAA batteries cannot.

Although lithium AAAA batteries are available, they are not directly compatible with other AAAA batteries due to the voltage difference.

AAA NiMH Battery

The following chart lists the most common chemistry types of AAA batteries:

Chemistry Common Name Rechargeable Typical Capacity (mAh) Voltage
Zinc Carbon R03, 24D No 500-600 1.5 V
Alkaline LR03, 24A No (Mostly No) 850-1200 1.5 V
Li-FeS2 FR03, 24LF No 1100-1300 1.5 V (1.8 V max)
Li-ion 10440 Yes 350-600 3.6 - 3.7 V
NiCd KR03, 24K Yes 300-500 1.2 V
NiMH HR03, 24H Yes 600-1300 1.2 V
NiOOH ZR03 No 1000-1200 1.5 V (1.7 V max)

AAA batteries are larger and more common than AAAA batteries, and are available in more chemistries, each having its own pros and cons.

AAA NiMH batteries offer good capacity combined with a large number of charging/discharging cycles and good discharge characteristics.

However, the actual capacity of the AAA NiMH batteries differs depending on their internal construction (high-drain, low-drain, multi-drain) and intended use.

AA NiMH Battery

The following table lists the most common AA battery chemistries and their features, including their most important feature, AA battery voltage:

Chemistry Common Name Rechargeable Typical Capacity (mAh) Voltage (V)
Zinc Carbon R6, 15D No 600 - 1600 1.5
Alkaline LR6, 15A No (Mostly No) 1800 - 2700 1.5
Li-FeS2 FR6, 15LF No 2700 - 3300 1.5 (1.8 max)
Li-ion 14500 Yes 600 - 2000+ 3.6 - 3.7
Li-SOCl2 (14505) No 2400-2700 3.5-3.6
Li-MnO2 CR AA No ~2000 3.0
NiCd KR6, 1.2K2 Yes 600 - 1000 1.2
NiMH HR6, 1.2H2 Yes 700 - 2800 1.2
NiOOH - No 2200 - 2700 1.5 (1.7 max)
NiZn ZR6 Yes 1500 - 1800 1.6 - 1.65

AA NiMH batteries are very popular AA rechargeable batteries, commonly found in remote controls, toys, game controllers, some flashlights, wireless devices, and similar.

Panasonic Eneloop AA NiMH battery, when charged with a proper charger can withstand up to 2000 charging/discharging cycles.

D-Cell NiMH Battery

The following comparison chart lists some of most common chemistries of the D-Cell batteries:

Chemistry Zinc-Carbon Alkaline NiCd NiMH
Typical Label R20, 13D LR20, 13A KR20 HR20, B006
Rechargeable No No (Mostly No) Yes Yes
Typical Capacity 8 Ah 12-18 Ah 2-6 Ah 8-12 Ah
Nominal Voltage 1.5 V 1.5 V 1.2 V 1.2 V

As one can see, the capacity of the NiMH D-Cell battery is comparable with the capacity of the alkaline D-Cell Alkaline battery. When the Alkaline D-Cell battery is discharged using higher currents, its actual capacity drops rather quickly.

Since the NiMH battery can be recharged many times, D-Cell NiMH batteries can be a rather cost-effective solution for cycling applications based on the D-Cell batteries.

9V NiMH Battery

The following comparison chart lists some of the most popular 9-volt battery chemistries with their most important features and specifications:

Battery Type Rechargeable Typical Capacity Nominal Voltage
Zinc-Carbon No 400 mAh 9V
Alkaline No (Mostly No) 550-600 mAh 9V
Lithium No 1200 mAh 9V
NiCd Yes 100-120 mAh 7.2, 8.4, 9.6V
NiMH Yes 175-300 mAh 7.2, 8.4, 9.6V
Lithium Polymer Yes 500-550 mAh 7.4V (11.1V)
Lithium-Ion Yes 600-650 mAh 7.4V (11.1V)
LiFePO4 Yes 200-320 mAh 9.6V

9V NiMH batteries have a nominal voltage of 9 volts, however, internally they may consist of 6, 7, or 8 cells connected in series in order to achieve 7.2, 8.4, or 9.6 volts, respectively.

Most 9V NiMH batteries feature 7 cells connected in series providing an actual voltage of 8.4 volts that slowly decreases down to the cutoff voltage of 7.0-7.7 volts, making NiMH 9V batteries compatible with 9V Carbon-Zinc, Alkaline, and non-rechargeable lithium (Li-MnO2) batteries.

tenergy sub c nimhNiMH batteries are also commonly used in other dimensions like C-Cell, Sub-C cells, 6V lantern batteries (5 NiMH cells in series), etc.

With a good discharge rate, affordable price, good energy density, NiMH batteries are still a very popular rechargeable battery type.

However, with advancements in technology and especially chemistry, lithium rechargeable batteries are replacing NiMH batteries in many applications.

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