This is great! I just looked up Volta and I see he was doing it a long time before anyone else.
Before 1800 even! Amazing.
Yes, I would say we add around 1/2 teaspoon of salty water per day (per tube) to keep the light going.
Am really just curious to see how long it can run for...
The whole area of bio-electricity was a big topic 200 years ago - the Frankenstein novel was based on real experiments! Volta and Galvani argued about whether the soul was electric ;-) Then the whole area got squashed out of mainstream. Later, even Mesmer did legit research, but is now assumed to be a joke. The elite that run publishing and research want to focus on the man-machine - sadly, most are too ignorant to even experience that this is not true.
Anyway, good luck with the experiments.
Something I would try is to connect one battery to one of those metal pyramid - if you have a Hall probe (fairly cheap) you can measure the magnetic fields, as will depend on where the connections are made on a pyramid - the resultant field is non-obvious, hence easier to measure than to calculate.
;-)
This is kinda interesting (altho not what I suggested, but related to the way energy scatters in a pyramis)
https://www.researchgate.net/publication/326530154_Electromagnetic_properties_of_the_Great_Pyramid_First_multipole_resonances_and_energy_concentration
(always worth searching for paywalled research articles, as often can be found free!)
If you skip through all the maths (unless you understand it) and look at the images, especially the 3rd set (i think) you will see how the largest field is in the centre and runs just below the surface of the ground. ;-)
So makes a huge difference having a pyramid on a table and actually on the earth!