We had in our mind many questions about the F5.
We needed 4 years to answer them all.
First, the biggest problem, was our trouble to understand, how the F5 works inside.
To find out why the F5 needs so much energy, we connected a F5 to a "volt Meter"( it is a voltage measuring instrument) .
We modified a F5, so that we could measure the "power hungry" while the F5 works.
The tests were taken with Alkaline batteries and rechargeable batteries.

We got amazing results.

Alkaline batteries lose the voltage strength permanently, while the F5 works.
The test proved, that the F5 still works , even if it comes to a drop down of the voltage value to 7.0 volt (for a short moment) .

If the F5 doesn't always need 12 volt to work, why couldn't we take 8 rechargeable batteries ?
To found an answer, we put rechargeable batteries into the F5 battery holder and connected the measuring instrument again.
Now comes the surprise.
Rechargeable batteries don't lose the voltage strength while the F5 works.
After countless trials we saw, that the F5 displays the " empty batteries" symbol, whenever the permanent voltage value
is 9.0 - 9.5 volt..
Unfortunately, 8 rechargeable batteries together have only 9,6 volt or charged with the "Ansmann-Powerline 4"
8 x 1,36 volt = 10,88 volt.
The voltage value ( 9,6 or 10,88 volt ) of 8 full charged rechargeable batteries have a too short distance to the " empty batteries symbol " voltage value of 9.0-9,5 volt.

Further