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

This is a question that arises very often in our daily work.

It is generally believed that Ni-MH batteries cannot replace disposable batteries due to their lower voltage. However, this applies only to certain devices - usually those with low power consumption and typically in configurations where batteries are connected in series of 3-4 pieces.
In high power consumption devices, the Ni-MH battery will even exhibit a higher voltage than an alkaline battery and will last significantly longer.
This is because the value of 1.2V is the average voltage during the operation (discharging) of the Ni-MH battery. A fully charged Ni-MH battery can reach a voltage exceeding 1.4V. Thus, it matches the voltage level of a new alkaline battery.

In summary - yes, in the vast majority of devices Ni-MH rechargeable batteries will perform at least as well as disposable alkaline batteries.

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

A load of 500 mA is quite demanding for alkaline batteries - this is a typical current draw for many toy flashlights, electric spice grinders, etc. - in such applications, alkaline batteries do not perform optimally. In the case of even more demanding devices - e.g., flashlights - the current draw is even higher (even multiple times) - in such applications, the performance difference between the Ni-MH rechargeable battery and the alkaline battery will be even greater in favor of the rechargeable battery. 

At a discharge current of 500 mA, a good rechargeable battery will last about twice as long as solid alkaline batteries. Testing under high load exposes the shortcomings of alkaline batteries and clearly indicates the superiority of nickel-metal hydride rechargeable batteries.

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

A load of 100 mA is more moderate - such a current draw is often found in the simplest flashlights, uncomplicated toys, wireless microphones, and lapel mics. In these conditions, the characteristics of the rechargeable battery are still more favorable compared to the alkaline battery. A freshly charged Ni-MH 1.2V battery maintains a higher voltage than a 1.5V battery for a significant part of the work cycle. However, the total working time may be slightly longer on a disposable battery. Additionally, it should be noted that the voltage on the Ni-MH battery decreases over time during storage, which is why devices that are used irregularly often work better on alkaline batteries.

Devices such as remote controls, weather stations, clocks, and electronic multimeters require even less power to operate (often much less) - in such devices, alkaline batteries usually last significantly longer and more predictably.

What stands out in both graphs is the flat discharge characteristic of the Ni-MH rechargeable battery. Rechargeable batteries in both cases maintain a voltage above 1.2V for most of the time. This characteristic has many advantages - for example, a remote-controlled model always accelerates eagerly and quickly, and a pepper grinder always operates with high, consistent efficiency. However, in the case of many devices, such a discharge characteristic makes it impossible to correctly read and assess the battery's charge state - depending on the device, the weak battery indicator does not light up at the right moment - either much too early or too late, at the moment when the device has already refused to cooperate. Therefore, despite the obvious advantages of rechargeable batteries, in some applications, standard alkaline batteries are more reliable and predictable.

Alkaline batteries vs rechargeable batteries - facts

To understand this issue well, one must be aware of the differences between disposable batteries and Ni-MH rechargeable batteries. We will explain the topic using the example of popular AA and AAA "batteries." As a representative of disposable batteries, we will refer to alkaline batteries - these are the most universal and fairly efficient disposable batteries, widely available on the market.
Basic technical data.

Alkaline battery:

• nominal voltage: 1.5V /cell,
• capacity up to about 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 production date,
• tendency to leak.

Ni-MH rechargeable battery:

• nominal voltage: 1.2V /cell,
• capacity up to about 1100 mAh for AAA/R03 and 2700 mAh for AA/R6,
• internal resistance 50-100 mΩ - suitable for high current draw devices,
• shelf life - not applicable,
• self-discharge of voltage over time.

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

In practice, 1.2V for a rechargeable battery is inherently the average voltage during the work cycle (during discharge in the device), while 1.5V is the output voltage (for a new, unused) alkaline battery. In most devices, the voltage ranges of batteries and Ni-MH rechargeable batteries overlap, and batteries do not have any advantage in this area.

The same applies to capacity - the higher capacity of alkaline batteries is achieved only during discharge at low currents - below 50 mA. At a discharge level of 500 mA (a typical current draw for many flashlights), the achieved capacities will be even half lower.

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

Another unfavorable feature for alkaline batteries is that every alkaline battery, even when stored/used under favorable conditions, will eventually leak - due to complete discharge or aging. Ni-MH batteries are very resistant to leaking - in their case, any leakage must be clearly provoked.

From the above, it would seem that rechargeable batteries have better parameters in almost every aspect. But is that really the case?

Unfortunately, the answer is not straightforward. Ni-MH rechargeable batteries are not without flaws. Rechargeable batteries exhibit slightly lower output voltage (at first) compared to alkaline batteries, and this voltage also decreases automatically even during storage. Some devices are unable to operate correctly at lower voltage levels - the situation worsens 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 and leading to a much smaller number of charge/discharge cycles. Rechargeable batteries, especially those with the highest capacities, can also be slightly larger (thicker) than disposable batteries, which in rare cases can also be problematic.

4 x AA / R6 everActive Ni-MH 2000 mAh rechargeable batteries ready to use "Silver line"

• excellent batteries at a low price
• 4pcs - factory consumer packaging - blister
• tested performance - real capacity
• pre-charged batteries, next generation made with Ready To Use technology
• highest quality of batteries confirmed by numerous tests

4,30 € gross 4,30 € net

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4 x AA / R6 everActive Ni-MH 2600 mAh rechargeable batteries ready to use "Professional line"

• excellent batteries at a low price
• 4pcs. - factory consumer packaging - blister
• tested performance - real capacity
• pre-charged batteries, next generation made with Ready To Use technology
• highest quality of batteries confirmed by numerous tests

5,80 € gross 5,80 € net

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4 x AA / R6 Panasonic Eneloop Ni-MH 2000mAh BK-3MCDE/4BE (blister)

• higher capacity min. 2000 mAh
• up to 2100 charging cycles
• retains 70% energy after 10 years from charging!
• operates in low temperatures down to -20°C!
• charged in the production process with solar energy

9,67 € gross 9,67 € net

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4 x R6 / AA Panasonic Eneloop PRO NEW Ni-MH 2500mAh BK-3HCDE/4BE (blister)

• highest capacity among new generation rechargeable batteries 2500 mAh
• retains 85% of energy after 12 months from charging!
• operates in low temperatures down to -20°C!
• charged during production with solar energy

12,10 € gross 12,10 € net

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

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