What Is a Battery? The Simple Explanation
A battery is energy in a parked car: stored chemistry that sits quietly until a circuit connects, and then turns into electricity on demand.
What is a battery in simple terms?
Think of it as a chemical pump: inside the cell, two different materials — the electrodes — sit in an electrolyte that carries ions between them. Connect a wire and the chemistry starts pushing electrons through it: that electron flow is the electricity. Disconnect the wire and the reaction pauses. Recharge and the same reaction runs backward, storing the energy again.
What is the difference between a cell and a battery?
The cell is the chemistry's natural unit — its voltage is fixed by the materials: roughly 2.0V for lead-acid, 3.2V for LFP, 3.6–3.7V for NMC. A battery is cells connected in series to reach a useful voltage: six 2V lead-acid cells make the 12V car battery, four LFP cells make a 12.8V pack (see series vs parallel).
What happens inside during discharge?
At the negative electrode, the chemistry gives up electrons; at the positive electrode, it takes them back — and the electrons travel the long way around through your circuit, doing the work. The electrolyte carries the ions between the electrodes to keep the charge balanced. In a lead-acid cell the acid gets weaker as it discharges, which is why a hydrometer can read the state of charge directly (see specific gravity).
What happens during charge?
Exactly the same reaction, driven backward by an outside voltage: the charger pushes electrons in the reverse direction and the chemistry re-stores them. The energy was never destroyed — a battery does not make electricity, it holds it, and every charge is a deposit back into the same chemical account.
The two chemistries at a glance
| Lead-acid | Lithium-ion | |
|---|---|---|
| Voltage per cell | ~2.0V | 3.2–3.7V |
| Energy per kg | ~30–50 Wh | ~150–250 Wh |
| Usable depth | ~50% | 80–90% |
| Cost | Lower | Higher |
| Extra electronics | None needed | BMS required |
The full trade-offs live in lesson 4.
Why This Matters
My position: The word 'battery' hides the one fact that explains everything else: the cell's chemistry sets its voltage, and everything from the 12V car to the EV pack is just cells arranged to reach a target. Learn the cell and you have learned the battery.
Why: Once the stored-chemistry model is in place, the rest of battery knowledge stops being memorisation and becomes prediction — why the acid weakens, why the voltage is fixed, why recharging works. One model, correctly built, explains a hundred facts.
My editorial view, not a purchasing guarantee.
Frequently asked questions
What is a battery in simple terms?
A battery converts stored chemical energy into electrical energy through a reversible reaction: discharge releases electrons through the circuit; charge runs the reaction backward. Two different electrode materials in an electrolyte set the cell's voltage, and that voltage is fixed by the chemistry.
What is the difference between a cell and a battery?
The cell is the chemistry's natural unit — about 2.0V for lead-acid, 3.2V for LFP. A battery is cells connected in series to reach a useful voltage: six lead-acid cells make the 12V car battery, four LFP cells make a 12.8V pack.
Sources
Cross-verified from the engineering references cited on the linked pages.
- Battery engineering references — cell chemistry and voltage.
- Manufacturer datasheets — cell and battery voltage ratings.
Next: Lesson 2 — voltage & amperage · Series index · Glossary · Last reviewed: 2026-09-17