Battery – How to Recycle Old MacBook Pro Batteries

The short answer would be no. A 5 y.o. battery won't last as long as a new(er) one. However, depending on if the original owner followed Apple's care instructions, and it doesn't have a high cycle count, it may not be much lower.

A lot of it depends on the care the battery was given. If the battery has just been sitting in a box this whole time, it's performance may be lower. Batteries need their "juices" (electrons) flowing in order for them to stay healthy.

On the other hand you have cycle count. A battery only can handle so many cycles before it wears out. Simply put, the higher the cycle count, the lower the performance.

Apple recommends storing a battery at 50% for extended periods of time. If it's fully charged or discharged when stored, this will again affect battery life.

Here is a comprehensive guide to Apple notebook batteries.

Of course, all this doesn't count any engineering changes that may have been made for the better in newer batteries.

If you connect 18 V to the power/ground pins, your Mac will be powered off the 12 V battery, but it won't charge: https://apple.stackexchange.com/a/132332/26231

To charge, the laptop needs to identify the charger by communicating over the signal pin in the middle. http://www.righto.com/2013/06/teardown-and-exploration-of-magsafe.html

Solution: Sacrifice an apple charger by cutting the cable and connecting the correct pins to your DC/DC converter. I recommend using the 45 W ones so your DC power supply doesn't have to be very big.