Hi Marco, yes, a battery can become swollen during storage. The swelling is due to gas build up in a battery that is deteriorating. It’s possible your MacBook Pro battery had started to deteriorate - particularly given its age - prior to or during the repair period.

Very interesting, Roger!

Experience with my iPhone 6, which has just 4 hours daily off-charge use, is that 2 years after Apple replaced the phone with a brand new (but old stock?) one due to a faulty charging circuit the battery health is still showing 100%. On the few occasions I haven’t charged it at all during the day but used it heavily, it typically has about 25% of charge remaining at the end of the day.

Maybe it helps that my phone is kept in an air conditioned office all day, and a cool bedroom at night while it charges, and I rarely use it while it’s plugged in to charge.

It wouldn’t be very difficult technically for Apple and other phone manufacturers to have a charging circuit that disconnects the battery once charged (optionally to a user-set level between the 40% optimum and 100%) and powers the phone directly from the charger. Batteries in phones that are mostly plugged in would last forever, but then there would be less incentive to replace your phone every few years, so it would hurt sales.

Hi Domenico, a swollen battery won’t necessarily catch fire but is at much higher risk of doing so. Many house fires have been started by batteries catching fire. Why risk it? Take your phone to a mall repairer and have them install a new battery for peace of mind.

Leaving your device plugged in forces it to drain and charge many times an hour, which can degrade the battery - this is rubbish. If the device is plugged in the battery will usually end up fully charged - which is not ideal as about 40% charge is best for battery longevity - but it won’t drain and charge continually. Instead, once the battery is fully charged it is essentially removed from the circuit and the charger powers the device.

Using a non-certified charging cable or adapter risks uncontrolled, uneven, or excessive charging that can cause damage or even result in fire - this is not quite true. All devices contain a charge controller that prevents overcharging regardless of the charger used. However, cheap chargers may subject you to the risk of electrocution, may produce ‘noisy’ DC that reduces the performance of the touchscreen, or may themselves catch fire. A damaged charger cable can also overheat and cause a fire.