Your friend didnt treat the battery very well and prematurely 'ended' its life.
Contact Apple for an appt. for free in shop full diagnostic and likely battery replacement.
Bad discharging or battery use conditions:
Heat (due to environmental conditions or due to rapid discharges from heavy use = gaming / video editing)
Rapid discharging of the battery frequently causes chemical changes over time in the battery leading to decreased capacity and resistance of current flow.
The very worst use of your battery is often draining the battery very low, and worse still letting it remain in such a state.
*Most long-term rapid damage to the battery occurs from discharging it with high loading (gaming) conditions but paramount is avoiding deep and frequent low DOD (depths of discharge) in use.
Undesirable charging or charged conditions:
High perpetual SOC (state of charge), where the battery is always or very often connected to charge
Parasitic loading where the battery is both usually on and charging or worse both always charging and in sleep mode, since this induces mini-cycling of the battery.
Bad general handling conditions:
Temperature use conditions when either too hot (95F and above) or too cold (50F and below)
Storing your battery away with a low charge (40% and less) long-term.
Considerations:
Your battery is subject to chemical aging even if not in use. A Lithium battery is aging as soon as its made, regardless.
In a perfect (although impractical) situation, your lithium battery is best idealized swinging back and forth between 25 and 85% SOC (state of charge) roughly.
Further still how you discharge the battery is far more important than how it is either charged or stored short term.
Ultimately counting charge cycles is of little to no importance. Abuse in discharging (foremost), charging, and storing the battery and how it affects battery chemistry is important and not the ‘odometer’ reading, or cycle counts on the battery.
Everything boils down to battery chemistry long term, and not an arbitrary number, or cycle count.
Keep your macbook plugged in when near a socket since in the near end of long-term life, this is beneficial to the battery.
