My daughter brought me her MacBook (one of the original duo laptops), and stated the battery wouldn't hold a charge, and the second the power was disconnected it shut down.
From the time the battery arrived (postal service 5 days) I had the computer up and running on battery power within 45 seconds. This included the time find a coin to open the battery compartment!
My daughter's not fussing, so mom is happy. Mom is happy I'm happy. When it's time to replace a battery just do it. It's the only cost other than the purchase price this computer has cost me since 2007(?)