An electric car is typically several hundred kilograms heavier than a combustion equivalent of the same size. The difference comes from the energy storage and from everything added to protect it.
Energy density is the root cause
Petrol stores a very large amount of energy in a small mass, and the tank holding it is light. Battery cells store a fraction of that per kilogram.
Electric drivetrains are far more efficient at turning stored energy into motion, which claws back part of the difference, but not nearly all of it.
The consequence is that giving an electric car a long range means carrying a great deal of mass, and there is no way around it with current chemistry.
The pack needs structure around it
A battery cannot simply be bolted underneath the floor. It needs a case stiff enough to resist intrusion in a side impact and to protect against debris from below.
It also needs cooling plates, coolant, wiring, contactors and a management system, all of which add mass before a single cell is counted.
Because the pack sits low and flat across the floor, the surrounding body structure has to be reinforced to carry loads that a conventional floor pan never handled.
Weight compounds on itself
A heavier car needs stronger suspension components, larger brakes, stiffer body structure and tyres with a higher load rating. Each of those additions weighs more than the part it replaces.
More mass also means more energy is needed for the same range, which means more cells, which means more mass again. Designers refer to this loop as the weight spiral.
Breaking the spiral is why so much electric vehicle engineering effort goes into structural efficiency, with the pack case increasingly doing double duty as part of the body.
What the extra mass changes on the road
Braking distances and cornering loads both rise, so the car needs more capable components simply to match the behaviour of a lighter vehicle.
Tyres wear faster, and the wear is aggravated by the instant torque available from an electric motor. Many electric models specify tyres built specifically for the loads involved.
Some of the weight is offset by its position. A pack under the floor gives a very low centre of gravity, which improves stability and resistance to rolling over.
The routes to lighter electric cars
Cell chemistries with higher energy density are the most direct route, since less mass of cells delivers the same range and the whole spiral unwinds.
Structural packs, where the cells form part of the load-bearing structure rather than sitting inside a separate case, remove a layer of duplicated material.
The simplest option is a smaller battery. Cars designed around realistic daily distances rather than maximum range end up lighter, cheaper and gentler on their tyres.