What are the differences between a 1.2V Ni-MH rechargeable battery and a 1.5V alkaline battery?

Comparison of the discharge characteristics of a high-quality Ni-MH (everActive Professional Line 2600) rechargeable battery against alkaline batteries from leading commercial brands. Discharge current: 500 mA, load character: continuous. 

A load of 500 mA is quite demanding for alkaline batteries - this is the typical current consumption of many torches, toys, electric spice grinders, etc. - In such applications, alkaline batteries do not work optimally. In the case of even more demanding devices - e.g. flash lamps - the current consumption is even higher (even repeatedly) - in such applications, the difference in performance between a Ni-MH battery and an alkaline battery will be even higher in favor of the battery. 

With a discharge current of 500 mA, a good battery will last about twice as long as solid alkaline batteries. The high-load test exposes the imperfections of alkaline batteries and clearly indicates the  advantage of nickel-metal hydride batteries.

Comparison of the discharge characteristics of a high-quality Ni-MH (everActive Professional Line 2600) rechargeable battery against alkaline batteries from leading commercial brands. Discharge current: 100mA, load character: continuous

A load of 100 mA is more moderate - this is often the power consumption of the simplest flashlights, simple toys, wireless microphones, microports. Under these conditions, the characteristics of the battery are still more favorable than those of an alkaline battery. A freshly charged 1.2V Ni-MH battery maintains a higher voltage than a 1.5V battery for a significant part of the duty cycle. However, the total operating time may already be slightly longer on a disposable battery. In addition, it should be borne in mind that the voltage on the Ni-MH battery decreases over time during storage, so often devices that are used irregularly work better on alkaline batteries.

Devices such as remote controls, weather stations, clocks, electronic multimeters require even less electricity (many times less) to work - in such devices, alkaline batteries usually last much longer and more predictably.

What is striking in both graphs is the flat discharge characteristic of the Ni-MH battery. Rechargeable batteries in both cases maintain a voltage above 1.2V for most of the time. This has many advantages - for example, the remote-controlled model always accelerates eagerly and quickly, and the pepper grinder always works with high, uniform efficiency. However, in the case of many devices, such discharge characteristics make it impossible to correctly read and assess the battery charge status - depending on the device, the low battery indicator does not light up at the right time - either much too quickly, or too late, when the  device no longer cooperates. Therefore, despite the obvious advantages of rechargeable batteries, standard alkaline batteries are more reliable and predictable in some applications.

Alkaline vs rechargeable batteries - facts

To understand this issue well, you need to be aware of the differences between single-use batteriesand Ni-MH batteries. We will explain the subject on the example of the popular AA and AAA "fingers". As a representative of disposable batteries, we will mention alkaline batteries - these are the most universal and quite efficient disposable batteries, commonly available on the market.
Basic technical data.

Alkaline battery:

• nominal voltage: 1.5V /cell,
• capacity up to approx. 1400 mAh for AAA/LR03 and 2900 mAh for AA/LR6,
• internal resistance >200mΩ - dedicated to devices with low or moderate energy demand,
• shelf life - usually 5-10 years from the date of production,
• tendency to spill out/leak.

Rechargeable Ni-MH battery:

• rated voltage: 1.2V /cell,
• capacity up to approx. 1100 mAh for AAA/R03 and 2700 mAh for AA/R6,
• internal resistance 50-100 mΩ - suitable for devices with high current consumption,
• shelf life - not applicable,
• self-acting voltage drop over time.

A cursory analysis of the above parameters will show that the batteries theoretically have a higher voltage and slightly higher capacities.

In practice, 1.2V for the battery is assumed to be the average voltage from the duty cycle (when discharged in the device), while 1.5V is the output voltage (for a new, unused) alkaline battery. In most devices, the operating voltage range of Ni-MH batteries and rechargeable batteries coincides and batteries do not have an advantage in this area.

The same is true of the capacity - higher capacity of alkaline batteries is achieved only when discharged with low currents - below 50 mA. With a discharge of 500 mA (typical current consumption for e.g. many flashlights), the achieved capacities will be up to half as low.

Ni-MH batteries show slight capacity losses under the same conditions - regardless of the discharge current. In addition, due to the much lower internal resistance, the voltage drop during operation is much smaller - especially in demanding devices.

There is one more infamous feature that speaks against alkaline batteries - every alkaline battery, even if stored/used in favorable conditions, will fail one day - as a result of its complete discharge or old age. Ni-MH batteries are very resistant to spilling - in their case, a possible leak must be clearly provoked.

From the above, it would appear that batteries have better parameters in almost every aspect. But are you sure?

Unfortunately, the answer is not clear. Ni-MH rechargeable batteries are not without their drawbacks. Batteries have a slightly lower output voltage (at the beginning) compared to an alkaline battery, in addition, this voltage drops automatically even during storage. Some devices are not able to work properly at lower voltage levels – the situation gets even worse over time.

Batteries are inherently high-current - using them in devices with very low energy consumption leads to a rapid increase in internal resistance - consequently shortening their lifespan leading to much fewer charge/discharge cycles. Rechargeable batteries, especially the highest capacity, can also be slightly larger (thicker) than disposable batteries, which can also be problematic in rare cases.

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4 x Panasonic Eneloop Ni-MH 2000mAh BK-3MCDE/4BE rechargeable batteries (blister)

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Author: Michał Seredziński
Copying the content of the text or its part without the consent of a representative of Baltrade sp. z o.o. is prohibited.

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