Lithium-ion battery

A lithium-ion cell stores energy chemically. Inside are two electrodes, a graphite anode and a metal-oxide or lithium-iron-phosphate cathode, kept apart by a thin porous separator and soaked in a liquid electrolyte. When you drive, lithium ions migrate from the anode through the separator to the cathode, while the electrons they leave behind take the external route through the inverter and motor; that electron flow is the current. Charging pushes everything back the other way. A single cell gives only a few volts, so a scooter pack strings a few dozen in series and a car pack several hundred, often in parallel groups too.

• Cells are grouped into modules, with cooling plates or air channels between them.
• Modules are bolted into a sealed pack under the floor of a car or under the seat of a scooter.
• A battery management system (BMS) measures every cell group's voltage and temperature, balances them and limits charge and discharge current.
• The BMS computes the state of charge shown as a percentage on the dash.

Two chemistries dominate Indian EVs. NMC (nickel-manganese-cobalt) stores more energy per kilogram and suits long-range cars. LFP (lithium-iron-phosphate) is cheaper, tolerates heat and full charges better and lasts more cycles, which is why Tata and several newer models have moved to it, while performance scooters such as the Ather 450 stay on NMC. Capacity is quoted in kWh and is the single biggest factor in price and range; range also falls in extreme heat and with fast driving. Batteries fade slowly with age and cycles, so manufacturers give separate warranties on the pack, usually far longer than on the rest of the vehicle. Fast DC charging heats the pack, so the BMS slows the charge as it nears full to protect it.