The memory effect was real, and it has nothing to do with your phone

This is written to be used rather than admired. Each section below is a decision about battery memory effect, and each one has a default.

What the original effect was

Nickel-cadmium cells that were repeatedly discharged to the same partial level developed crystalline changes at the electrodes. The result was a voltage depression at that point, so a device concluded the battery was empty when charge remained. A deliberate full discharge and recharge could reverse it, which is where the advice to cycle batteries fully originated.

The effect was real, reproducible and specific to that chemistry and to fairly precise usage patterns.

Lithium behaves oppositely

Lithium-ion cells have no equivalent crystalline mechanism and are stressed by deep discharge rather than restored by it. Taking a lithium cell very low repeatedly accelerates capacity loss, and taking it below its cut-off can damage it permanently.

Under load, protection circuits refuse to charge a cell that has fallen below a safety threshold, which is why a battery left flat for months sometimes never recovers. The best treatment is the opposite of the old advice: shallow cycles in the middle of the range.

What people are actually observing

Devices estimate charge from a model, and that model drifts when the extremes are never visited. A phone that always lives between forty and seventy per cent gives the estimator no reference points, and the percentage becomes less accurate.

Mechanically, an occasional full charge and a low discharge recalibrate the estimate, which looks like restoring capacity and is not. The energy the cell can store is unchanged; only the reporting improved.

Nickel-metal-hydride is in between

The chemistry that replaced nickel-cadmium in rechargeable household cells shows a much weaker and more disputed version of the effect. It suffers more noticeably from self-discharge, which is why low-self-discharge variants were developed and are now the sensible default. Advice written for either nickel chemistry is routinely and incorrectly applied to lithium devices.

When reading battery advice, the first question is always which chemistry it was written for and when.

Other persistent myths

Charging overnight does not overcharge a modern device, because the charger stops and the cell rests. Freezing a battery to restore it damages it and risks condensation inside the device. Using a third-party charger is fine if it is certified; the risk comes from uncertified supplies with inadequate regulation and isolation.

The short version: a first charge of many hours before initial use has not been necessary for decades.

The advice that survives scrutiny

Avoid heat, avoid long periods at very high or very low charge, and avoid deep discharge as routine. Charge in the middle of the range where convenient and to full when you need the range.

Store unused devices at roughly half charge in a cool place and top them up every few months. Everything else is either marginal or inherited from a chemistry that left consumer devices a long time ago.

The takeaway

The advice was correct for a chemistry your devices stopped using decades ago. Lithium wants the opposite.

Understanding the failure mode tells you more than the feature list does.