One particularly persistent battery myth is that you need to occasionally fully discharge and recharge to erase “battery memory.” This couldn’t be more wrong for lithium-ion batteries. It’s a leftover myth from lead-acid cells, and is actually quite undesirable to charge your modern smartphone in this way.
Partial charging is just fine for lithium-ion batteries and can actually have some positive benefits for cell longevity. To understand why, it’s important to appreciate how a battery charges. When closer to empty, Li-ion batteries draw in a constant current and operate at a lower voltage. This voltage gradually increases as the cell charges up, leveling off at around a 70 percent charge before the current begins to fall until the capacity is full.
Using up just 20 percent of your battery between charges isn’t going to be practical for most people, but topping up when you’ve used about half will see a notable improvement in your battery life over the long term, especially if you avoid charging up to full each time too. The bottom line is that small regular top-ups are much better for Li-ion batteries than long full charge cycles.
A final point worth mentioning is parasitic load. This occurs when the battery is being drained significantly at the same time as being charged, such as watching a video or gaming while charging.
Parasitic loads are bad for batteries because they distort the charging cycle and can induce mini cycles, where part of the battery continually cycles and deteriorates at a faster rate than the rest of the cell. Worse still, parasitic loads occurring when a device is fully charged also induce higher voltage stress and heat on the battery.