you cannot reverse battery chemistry damage. You can increase its charge time use by verifying what is draining power.
1. did you often drain the battery very low?
2. did you often /always have your macbook on charge,......or did you often / always BOTH have your macbook on charge AND in sleep mode?
1 or 2 are harsh on the battery chemistry and therefore its longevity
all batteries are consumables meant to replaced either in their own "due time" or early due to abuse / misuse.
Occasionaly i would drain the battery very low
NEVER do that to a lithium battery. Its a perfect way to cause premature death of a lithium battery.
All batteries in any device are a consumable meant to be replaced eventually after much time, even under perfect use conditions.
If the massive amount of data that exists on lithium batteries were to be condensed into a simplex, helpful, and memorable bit of information it would be:
1. While realistically a bit impractical during normal everyday use, a lithium battery's longevity and its chemistry's health is most happy swinging back and forth between 20% and 85% charge roughly.
2. Do not purposefully drain your battery very low (10% and less), and do not keep them charged often or always high (100%).
3. Lithium batteries do not like the following:
A: Deep discharges, as meaning roughly 10% or less on a frequent basis.
B: Rapid discharges as referring to energy intensive gaming on battery on a frequent basis (in which case while gaming, if possible, do same on power rather than battery). This is a minor consideration.
C: Constant inflation, as meaning always or most often on charge, and certainly not both in sleep mode and on charge always or often.
From Apple on batteries:
"Apple does not recommend leaving your portable plugged in all the time."