Differences between disposable and rechargable batteries?

[leadpaint]

I have noticed that disposable batteries are rated at 1.5 volts, while rechargables are rated at 1.2V. Why is this, and does this make a difference to the device using the batteries?

Thanks in advance.

 

[Rubycon]

Battery chemistry determines what its terminal voltage is. Nickel Cadmium and Nickel Metal Hydride rechargeable cells are 1.2V whereas the common dry cell is 1.5V.

Battery primer

 

[Modelworks]

It can make a difference in the device. Devices like cameras are designed to use a certain voltage at a specified current. If the voltage drops then the device uses more current to make up for the difference, killing the battery faster. So comparing a alkaline at 1.5V to the same capacity rechargeable isn't valid because the 1.5V will always last longer. You need a higher capacity rechargeable for it to be equivalent to the 1.5v.

Use the old amps x volts formula for a quick comparison.
1.5v , 2800 mah alkaline battery = 4.2 watts possible power from each battery
NiMh 1.2v , 2800 mah rechargeable battery = 3.36 watts possible power

Notice they like to sell rechargeable batteries as 2800 + mah to make it seem to compare to the alkaline, but they don't mention the voltage.

It would take a 3500mah NiMh to equal a 1.5v 2800mah alkaline. That will never happen with NiMh as the battery size would be too large to work in devices.


They also use other tricks , like Energizer was selling rechargeable D batteries. On the inside was a plastic holder with a C cell inside.

 

[Rubycon]

It gets complicated when you have high current loads like photoflash. The alkaline will have good results with medium loads. As current draw increases the alkaline's terminal voltage sags considerably compared to the nickel metal hydride whose lower internal impedance acts to stiffen up its terminal voltage with less sag under load. This is why a professional strobe will cycle faster with four 1.2V nimh cells vs. four alkalines even though the alkalines have higher terminal voltage.

Proper matching of your device is important in this regard to get the best capacity out of a given battery technology.

Originally posted by: Modelworks

They also use other tricks , like Energizer was selling rechargeable D batteries. On the inside was a plastic holder with a C cell inside.

I've seen worse - how about a 2500mAh AA inside a D sized casing? It's pretty easy to tell just by looking that the capacity. A true high end nimh D cell should have capacity in excess of 10Ah!

 

[leadpaint]

Good info, thanks.