Fresh fruits can be used as batteries for glowing bulbs, but how this is possible? I mean how can electric charges flow through fruits? Do they contain chemicals like cells?
[Physics] How to a fruit be used as a battery cell
batterieselectricityelectrochemistry
Related Solutions
So technically, in those physics examples the voltage isn't fixed in those batteries. The potential drops, just very slowly for small currents. For example, if the voltage is 12V and some small current flows, the voltage drops. However, it drops to like, say, 11.9999935434V or whatever. So for the problem you don't really care and you just assume 12V. Eventually, once the current has run long enough it will become noticeable in practice that the voltage is not 12V. And that's when you need to recharge the battery (if rechargeable) or get a new one.
The movement of charges, that is the current, when the circuit is closed is due to electrochemical reactions taking place at the anode and cathode.
Very simply put, the first reaction is an oxidation reaction, e.g. taking place at the cathode:
$$\text{A} \to \text{A}^+ + e^-\tag{2}$$
Secondly at the anode a reduction reaction takes place:
$$\text{B} + e^- \to \text{B}^-\tag{3}$$
So the overall reaction is:
$$\text{A}+\text{B}\to \text{AB}$$
A battery has ran 'out of juice' as you put it, when $\text{A}$ and $\text{B}$ are sufficiently depleted (reacted away) There is then nothing left to oxidize or reduce and no current can be produced.
One of the most common type of cells is the manganese/zinc cell. In it, zinc metal is oxidized to $\text{Zn}^{2+}$ and manganese dioxide ($\text{MnO}_2$) is reduced to $\text{Mn}$ $\text{ III}$.
Note also that a battery is made up of usually one of more identical cells, arranged in series or parallel. It's the cells we're interested in here.
In a more sophisticated interpretation, the reaction: $$\text{A}+\text{B} \leftrightarrow \text{AB}$$ is considered an equilibrium reaction governed by:
$$K=\frac{a_A a_B}{a_{AB}}\tag{1}$$
where the $a$ are the chemical activities of the reactants (like concentrations) and $K$ the equilibrium constant.
When the battery is new (or fully charged) the reactants are far from equilibrium. On closing the circuit, the oxidation and reduction reactions then proceed until the condition $(1)$ is met.
In the case of a rechargeable cell or battery during recharging, a current is ran through the cells/battery that causes $(2)$ and $(3)$ to proceed from right to left. The original concentrations of $\text{A}$ and $\text{B}$ are thus restored.
Best Answer
Fruits can be used as part of a battery. Fruits typically have a weak acid in an aqueous solution. Because the acid can dissociate, it is usable as a cell's electrolyte, allowing a net migration of ions from one electrode to the other.
You would still need appropriate electrodes, which contain materials that participate in the chemical reactions to produce the electricity.