Four MacBook battery habits with no evidence behind them
Calibration cycles, running the battery flat, avoiding fast chargers and worrying about Service Recommended, checked against Apple's documentation and published research.
Battery advice travels from one generation of devices to the next long after the chemistry has changed. These four habits are still common, and none of them holds up against Apple’s own documentation or published research.
1. Calibrating the battery every month
The habit: run the battery from 100% to 0% and back, to “calibrate” it.
Calibration corrects the gauge, the estimate of how full the battery is. It does not improve the battery’s health (Battery University, BU-603). A Mac also handles it alone: with a charge limit set, macOS charges to 100% now and then to keep its reading accurate.
2. Running the battery down to 0% before charging
The habit dates from nickel batteries. Apple says there is no need to discharge fully before recharging a lithium-ion battery. In lab tests the opposite was true: Preger and colleagues found that deeper discharges wore cells out faster than shallow ones. Plug in whenever it suits you.
3. Avoiding the bigger charger
The worry: a 140 W charger wears the battery faster than a 70 W one.
Harm from fast charging is shown for currents well above what laptops use (Battery University, BU-401a). For laptop chargers there is no good data either way, so there is no reason to prefer the slow one. Use whichever is convenient.
4. Treating “Service Recommended” as an emergency
When macOS reports the battery condition as Service Recommended, Apple says you can safely keep using the Mac. The battery holds less charge than it did when new, and that is all the message means. Apple designs MacBook batteries to keep up to 80% of their capacity at 1000 cycles under ideal conditions, so the message arrives eventually on every Mac.
What does have evidence behind it
- Keeping the Mac out of heat, especially while it charges.
- Reducing the time spent at full charge, with a charge limit or Optimized Battery Charging.
- Storing an unused Mac at about half charge.
Dotwatt’s tips come from the same sources, and each one says what is known and what is not.