Why are Rechargeable Batteries only 1.2V?

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Why Do Rechargeable Batteries Have Lower Voltage Than Alkalines?

Find out everything you need to know about why the lower 1.2 volts in rechargeable batteries still manage to outperform the 1.5 volts in alkaline batteries.

If you’re just beginning to research and explore the world of NiMH rechargeable batteries, then you may be a little intimidated by all the numbers and ratings you read about online. When comparing rechargeable batteries to disposable alkaline batteries, you’re bound to read about "voltage depression" and mAh (milliampere-hour) ratings, both of which are new technological specifications that the average consumer never has to consider when purchasing alkalines.

Also, as electronics become increasingly more high performance, consumers like you and I are beginning to take notice of output voltage on batteries as well, since some electronics require certain voltage levels in order to function at optimal levels. Recently, questions have arisen in the electronics community about the output voltage of rechargeable batteries, and how it measures up with disposable alkaline batteries. You yourself may have noticed that, while alkaline batteries have a voltage output of 1.5 volts, NiMH rechargeable batteries only output 1.2 volts of power. Given this lower level of voltage, a question arises: does the .3v you lose with NiMH rechargeable batteries negatively affect the performance of your electronics?

Simply put – no! But here are the facts and data that explain why this is the case.

First, it’s inaccurate to say that alkaline batteries manage a voltage output of 1.5 volts. While it is true that the average alkaline battery has an output of 1.5 volts when it is new, in reality, an alkaline’s lifecycle is such that it quickly drops from 1.5 to 1.0 volts before dying out. Because of this, the average output of an alkaline battery is the same as that of an NiMH rechargeable battery: about 1.2 volts. An alkaline battery really only outputs a 1.5 V voltage at the very beginning of its use. Soon after, it begins to decrease down to well below 1.2 V, bottoming out around 0.6 V. Quite low! 

Actually, most of the basic consumer electronics function normally using battery power with an output between 0.9 V and 1.5 V. However, unlike alkaline batteries, where the voltage drops quickly and gives you performance that’s well below 1.5 volts, NiMH rechargeable batteries, on the other hand, provide a steady stream of voltage from the beginning of its charge until the very end – about 1.25 V. And because of the manner in which NiMH rechargeable batteries discharge, the voltage output does not “slide” down consistently as the batteries are being used; rechargeable batteries offer a very stable voltage output and abruptly cut off when they are completely spent.
In this way, despite the lower voltage, consumers actually get a steadier, more reliable power output from NiMH rechargeable batteries. That is why the latest rechargeable batteries will actually outperform alkaline batteries in equipment calling for a constant and high level of energy input, such as digital cameras, flashes, camcorders, computers, portable phones, CD players, toys, gadgets, and anything else that takes batteries.

All of this being said, there are some electronic gadgets that can slightly benefit from the initial 1.5-volt output of a brand-new alkaline battery. For example, a small radio or flashlight will give you a short window of increased performance at 1.5 volts, versus the 1.2 volts of a freshly charged NiMH rechargeable battery. This is because, in both cases, more voltage means a brighter light or farther-reaching reception.

But while this may be the case, there is also another consideration: because alkaline batteries feature a steady decline in voltage, you’ll also see an equally steady decline in light and radio reception, respectively. With a rechargeable battery, the initial light or reception may not be as strong, but it will give steadier power over an extended period.

Finally, there is one other difference in the output voltages of rechargeable and alkaline batteries that needs to be considered as well. Because the voltage of an alkaline battery drops at a very predictable rate: 1.5 volts - fully charged, 1.25 volts - 50% charged, 1.0 volts - at the end of its lifecycle, many electronic devices can track the remaining power in a disposable battery, keeping you informed as to when you need to change the batteries. This is particularly helpful for digital cameras and even game controllers like the Wiimote. NiMH rechargeable batteries, however, cannot be tracked by electronics, since their output remains virtually at 1.2 volts until it is nearly completely discharged. This can be a bit of a disadvantage if you rely on keeping close track of an electronics’ battery power.

Chances are, however, if you use rechargeable batteries on a regular basis for all of your electronics, most likely you have a fresh set of batteries on hand when your digital camera, Wiimote, or other electronic device goes dead. Regardless, if you rely on electronics that use batteries, it’s good to fully understand how output voltages between rechargeable and alkaline batteries can impact your gadgets’ performance.

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