A decade ago nicad (nickel cadmium) and nickel-metal hydride rechargeable batteries were pretty common in phones and laptops, but with the push for more energy in lighter, smaller mobile units, lithium ion batte. Rechargeable batteries power devices the same way that disposable batteries do — by chemical reactions at the positive and negative electrodes. Those reactions allow positively charge. Back in the day, we all dutifully let our phones and seven-kilogram laptops go totally flat. The chemical reactions that are at the heart of all batteries generate some heat, and lithium-ion batteries have made headlines when that heat gets out of control and they catch fire — mos. From the moment they're made, lithium ion batteries start losing their ability to store charge and generate a voltage over time. It's called ageing, and it happens whether they're being use.
