BATTERY longevity and how the cells degrade obviously determines the useful life of electric cars and how much someone will be prepared to pay for it second-hand.
This in turn determines the cost of ownership and monthly costs on a personal contract purchase plan.
At the moment, the values of used-battery cars are frustratingly low because the second-hand market does not understand the technology, and is concerned with what happens when battery warranties expire.
Lithiam-ion batteries contain five main components: cathode, anode, separator, current collectors and electrolyte.
When the battery is discharged, the lithium ions move from the anode to the cathode, generating a flow of electrons through the device.
In a lithium-ion battery this process is reversible over many cycles and years, and Li-ion batteries carry more charge for less weight than alternatives such as lead-acid or nickel-metal-hydride cells.
To prolong the lifetime of these batteries, car battery manufacturers employ additives to the electrolyte or coatings on the electrodes to try to protect them against degradation.
Some experts have advised that electric car batteries should only be charged to 80 per cent, as going the whole way stresses the cathode.
Lithium-ion batteries are not flawless environmentally, either in the electricity that recharges them or the elements that go into their make-up.
Lithium is dangerous, reactive in air and hard to recycle, so lots of batteries end up in landfill simply as a safety measure.
Battery-electric cars are going to have to be much more desirable as a used buy if this technology is going to get fully off the ground, and that depends on understanding how to look after them.