Margen
Your phone doesn't need you to let it die. Running the battery down until it shuts off only adds wear, and it buys you nothing in return. The ritual of squeezing it to zero comes from a kind of cell almost nobody has at home any more.
1. Stop chasing zero.
The memory effect belonged to nickel-cadmium, the grey rechargeables in the cameras and drills of forty years ago. If you plugged them in halfway down every time, they ended up behaving as though that halfway point were their whole capacity. That is where the family habit of draining a battery before charging it came from, and it has not moved since.
Most of today's phones, laptops and scooters run on lithium-ion, which is a different chemistry. A deep discharge costs it working life.
2. Yes, they did find memory in lithium too. And it doesn't say what you think.
In 2013, a team at the Paul Scherrer Institute, the big Swiss public laboratory, published in Nature Materials a memory effect in LiFePO4 — the lithium in e-bikes and campervans, not the one in your phone — and a single partial cycle was enough to trigger it. The work was done with Toyota's research laboratories.
What they found is a small shift in voltage. That throws off the system that translates voltage into a percentage, and the device can miscalculate how much charge is left. It does not eat capacity. The finding does not rescue the old advice: it makes it worse, because it teaches you that the number on the screen is the first thing that lies.
3. Swap one long discharge for several short ones.
Here it helps to know what a cycle is, because it isn't plugging in the cable: a cycle is one full charge added up, so two half charges count as one, not two. Battery University, the technical site of the instrument maker Cadex, has been publishing its measurements for years: it counts how many cycles a lithium NMC cell — nickel, manganese and cobalt, the one in phones — survives before it drops to 70 % of its capacity.
Emptying it completely every time: around 300 cycles. Using three fifths of it: around 600. Using a fifth and plugging in: around 2,000. It is the same cell; the only thing that changes is how far down you let it go. The figures change with the chemistry, the temperature and the test protocol. The order between them does not.
4. Use the 80 % cap on ordinary days.
Plenty of new phones come with a limiter that stops the charge at 80 %. Stopping short of the end multiplies the cycles. Battery University's voltage table shows it plainly. At 4.20 volts per cell, which is the 100 % we all grew up with, you get between 300 and 500 cycles. At 4.00 volts you are left with 73 % of the energy and reach between 850 and 1,500.
No phone lets you pick volts, so the 80 % switch is the domestic version of that table. The 80 % cap gives you more months of battery. On days when you need the whole range, you turn the cap off and that's that.
5. Heat does more damage than any ritual.
Above 30 degrees a battery is already in the hot zone. Heat with the battery full does more damage than heat alone. Stored for a year at full charge, at 25 degrees it keeps around 80 % of its capacity. The same battery, the same year, at 40 degrees: 65 %.
Translated to your house: the phone charging on top of the radiator, or inside the car in August with the cable plugged in, ages faster than it would if you used it non-stop.
6. If you are putting it away for months, leave it at half.
A laptop about to spend the winter in the loft is ruined more by sitting there full and warm than by being used. Charge it to about half before you put it away, and find the coolest spot in the house. The box room is not it. And do not store it at 0 %: a battery left empty for months may never wake up again.
Turn on the 80 % cap if your phone has one, plug it in before it shuts off, keep it out of the sun and off the radiator, and stop draining the battery just to keep up the old ritual.