Why do some hi-tech devices with fully-drained, permanent lithium ion batteries need some battery charge before working even when you plug them in?



I’ve noticed this with ipads and iphones. If it’s completely drained and you plug it in, you still can’t turn it on for a few minutes. I don’t know if the battery is part of the standard circuit powering the thing or what.

In: Technology

It’s more than likely a hardware encoded safety measure. Draining lithium ion batteries completely actually damages them. So when a device says it’s at “1%” the more accurate assessment is that it may have somewhere between 3-5% charge left but it’s encoded not to power on due to risk of battery damage. At least I know iPhones do this I’m sure most other devices do except for maybe really cheap ones.

The battery has to deliver a minimum voltage for the device to work properly. The voltage that a battery delivers decreases as its charge decreases, so if the charge is too low, the voltage will be too low.

While it would be more convenient for a user for the charging circuit to have the ability to bypass the battery and power the device directly, it is more complicated and therefore more expensive (and bulkier and heavier) to do so. With most modern electronics, when you plug them into a charger, it’s not as though the electronics are directly connected to the power source. Instead, the battery is directly connected to the power source and the device is separately connected to the battery. This has a couple of advantages, including helping to mitigate possible damage to the main electronics of the device if it’s plugged into a bad power source. But it does mean that the battery has to be charged enough to deliver sufficient voltage for the device to operate, which (depending on the design of the device and the battery display) might very well mean that it needs to be at 5% battery to turn on. The boot process draws more current, generally speaking, than simply staying on, which it very low battery might mean that the battery simply can’t deliver sufficient current to turn on but can deliver sufficient current to stay on for another few minutes.

Electronic devices like phones, tablets or laptops don’t have a constant consumption of power. So when it has to do a lot of things (like startup or play movies and games) the device requires a lot more power than “normal”. For laptops, the chargers are sufficient to run the device at full power mode and still charge the battery. For smaller devices (especially older ones with older USB), the maximum power consumption can exceed the power provided by the charger.

In cases like this, if the phone tried to power up with a fully discharged battery, it would boot up halfway, then shut down since the charger cannot provide enough power to complete the boot up cycle. This becomes an endless cycle of boot up halfway, shut down and then trying to boot up again. To avoid this, manufacturers will design the product that prevents startup until the batteries achieve a charge sufficient to at least get through the startup cycle.