Some of the retail options from non-computer sources who do not guarantee they have been
tested to actually work in specific models of computers, can leave you in the lurch; some only
will guarantee the battery is OK, and a replacement is the only remedy.
OtherWorldComputing is a reputable source for Mac-centric users for decades; so they will
try and often succeed in customer service & help you even before you buy; even if you don't.
I'd avoid the 'battery plus' kind shopping mall or 'walmart kind' of places to get cloned batteries.
The battery internal circuitry that supposed to co-ordinate charging could be substandard also.
{They'd tried to sell me incorrect voltage batteries and argued I did not know what my Lumix
camera used for an original battery; while it was in my hand. The choice offered me there was
so far wrong, but their guarantee would not have repaired or replaced my digital camera either.
I ordered correct quality batteries online from a reputable company that uses japanese cells.}
The battery is a part of the charging and power system, so be sure the magsafe adapter, the
battery and the magsafe board are all working properly; this may require diagnostic testing.
•Apple Portables: Troubleshooting MagSafe adapters - Apple Support
•About Mac notebook batteries - Apple Support
•Apps can affect Mac performance, battery runtime, temperature, and fan activity - Apple Support
http://www.apple.com/batteries/maximizing-performance/#macbook
In any event...
Good luck & happy computing! 🙂