Alkaline 1.5v VS. NiMH 1.2v

When using 4 AA alkalines, the voltage is 6 volts, with NiMH it's 4.8 volts. Obviously, it would take 5 nimhs to equal the voltage of 4 alkalines. This leads me to my question, and please forgive me that it is not flashlight related although the same principles can be applied to them.

I have pair of Midland 2-way radios. They come with NiMH rechargable battery packs. The packs are basically 5 AAA cells enclosed in a plastic shell. The voltage is 6v with stated capacity of 700mAH. This is not very much capacity in my opinion. One has the option of not using the battery packs and using 4 AA alkalines instead which will give you 6v and longer running time?

Would it be wise to use 4 AA NiMHs instead? This would obviously bring the voltage down to 4.8, but with the advantage of having 2500mAH. Do you think, or do you know if this reduction in voltage would diminish efficacy of my 2-way radios? The radios are rated at 5 Watts, which I cannot prove nor disprove. They also have a very ambitious 14 mile rating (4-5 miles max realistically). I hypothesize that because of the lower voltage, signal strength would be decreases and therefore effective range of the units will also be decreased.

I'm worried that the 20% reduction in voltage with the 4 NiMH will have a significant impact on signal strength. Is my concern legitamate? Any help apprciated.

I was wrong ...

If you can fit 4xAA I would go that route w/ 2700mah.... if you can't then use 1000mah AAA's....

jar3ds is wrong.

If you run one million AAA batteries in series at 1.2 million volts will STILL only have 700mAh! Just like one million AAA batteries running 1.2 volts in parallel will still have only 1.2 volts! at (though 700 million Milliamp hours capacity). Miliwatt hours might be a better comparison to the apples and oranges you guys are trying to compare.

The 4 AA alkaline / NiMh option should add a bit to the runtime because of the increased capacity of the cells. You should be able to use NIMH batteries in it without much ill effect. Alkaline batteries settle at about 1.2 volts miday through their life anyway. Given the choice I'd pick the 4 x AA option anyday.

NiMH are roughly 0.05V higher than NiCad due to the difference in chemistry, so 4 of them would give you about 5V average over the battery life. Alkaline start at 1.5 to 1.6 volts but are considered end of life at 0.9V, giving an average over the battery life of about 1.3 volts per cell, or 5.2 volts total-not much more than NiMH. The simple fact is that the radio must be designed to work with alkaline not just when they're fresh, but when they're near the end of their life. Because of this fact, 4 NiMH should work just fine if not better. In fact, if the radios are rated at 5 watts then this implies a current drain of at least 1 amp from a 5V battery pack. AA alkaline actually have a lower voltage than NiMH even when fresh at current drains much above about 300 mA.

what kind of AA rechargeable has 700mah?(the nimhs kind)

Ches: The AAA have 700mah.

Thanks for the above responses. It totally makes sense now, since I didn't consider the voltage sag. I definitely feel better with 2500mah of capacity.

Just use NiMH instead of alkaline and you'll be fine. Don't worry about the voltage. Alkaline is 1.5V when brand new and decreases as you use it, averaging maybe 1.2-1.3 volts over the whole discharge, with some juice left even at 0.7 volts. Any decent equipment designed for alkalines should be designed to work as low as 1.0 volts per cell or lower, preferably below 0.9. NiMh is about 1.4V when fully charged, drops very quickly to about 1.3V, and then falls from 1.3V to 1.2V over the discharge and is pretty pooped by the time it gets below 1.2V. Basically you should be able to directly replace alkaline with NiMH without voltage problems in well-designed equipment.