Do nickel metal hydride batteries (rechargeable) have more/less power than alkaline?

Do nickel metal hydride batteries (rechargeable) have more or less power than alkaline batteries? Just because they can recharge isn’t that great unless they has a sufficient power supply.

Typically, alkaline batteries are not rechargeable. The most popular chemical compositions are nickel-cadmium, nickel-metal-hydride, and lithium-ion. As far as power is concerned, all types can be constructed with various amp/hour capacities.

The decision is based on initial cost, charge time, life cycle, and available power.

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It’s variable, but the 2200 mAh NIMH batteries I have last a lot longer than any alkaline that I’ve ever used.

In my gps which also times battery life alks get about 19hrs, Nimh (1600 mAh) get 12 hrs. But this is a low drain device and I understand that Nimh does better at higher drains (and NiCd does even better).

When I was reviewing batteries used in a certain palmtop computer (it used two AA batteries) I compared running times for several brands of NiMH batteries, rated from a low of 900mAh to a high of 2200mAh, and it turned out that a good rule of thumb was that alkaline batteries performed like they were 4000mAh NiMH batteries – by which I mean they lasted slightly less than twice as long as the 2200mAh NiMH batteries, slightly over four times as long as the 900mAh batteries, about three times as long as the 1350mAh batteries, etc. The results were pretty constant for various brands of alkaline batteries – Duracells and Energizers and Toshibas and Kirkland Signatures all seemed about the same. I wish I could find the spreadsheet I created at the time – it produced some pretty interesting graphs from the data.

You have to be careful when making comparisons, since alkalines tend to lose voltage at a constant rate, while NiMH batteries will sit at a particular voltage for a while and then drop off drastically near the end of their life. So take that into account.

It greatly depends on the usage. In some types of use (high drain, like digital cameras) NiMH will outlast Alkyline by a huge margin. In other usages (like flashlights I believe) Alkyline will last longer. There is no one simple answer.

This isn’t quite right. The batteries don’t lose voltage, what really happens is the internal resistance goes up. As the internal resistance increases, the voltage across a given load decreases. However, if you had an ideal, infinite-resistance voltmeter, you’d see that the open circuit voltage remains constant. Otherwise, it’s as you say. Alkalines have a slow, consistent discharge curve, whereas NiCd and NiMH cells have a nearly constant internal resistance right up to near the end, when they suddenly drop off. This makes those rechargeable chemistries unsuitable for things like smoke detectors, when you want a suitably long warning that the batteries are failing.