[Elecraft] Re: Rechargeable NiMH Cells

[Pieter Meiring]

> In a message dated 31/05/05 08:37:43 GMT Daylight Time, kd3jf at hotmail.com
> writes:
>
> To  all..... I ordered 8 rechargable batteries from ZBattery at a good
> price.
>
> I have stayed away from rechargable batteries because of the 1.2 volts per
> AA battery. However these are the high capacity batteries <<2450 amp  hr.>>
> What do you think for my K1? At 9.6 volts I am not sure what  power output
> I will have... If it doesn't work out for the K1 I can always  use them in
> my dig. camera!
>
>
>
My 2c worth:

Modern high capacity NiMH batteries (I have about 30 of them, up to 2500mAh AA 
size, for camera, CD player, GPS, etc...) seem to have to following 
characteristics:
* Fully charged voltage of about 1.35V
* After initial current drain, this drops to about 1.25V and stays there until 
about 90% drain.
* They lose about 10% of their charge per week on the shelf.
* They ideally need an "intelligent" microprocessor controlled charger for 
best results.
* The largest capacity AA ones are quite a tight fit into AA holders.

In my experience, rechargeable NiMH AA batteries are better than Alkaline 
cells despite their lower initial operating voltage. Alkaline cells drop 
their voltage more rapidly in the second half of their discharge cycle and 
tend to give lower power overall. I tend to make up a battery with an extra 
cell to offset the voltage difference.

Lithium cells have a higher capacity and hold their voltage well throughout 
the discharge cycle but are a bit more expensive.

Li-Ion/Li-Polymer rechargeable cells are not, as far as I am aware, available 
in AA size commercially (yet) and also have other problems. They need a 
special dedicated charger and cell life is limited to 18 months to  2 years 
regardless of use due to cell degradation.

Pieter