Can I safely use my Macbook battery on another MacBook? A friend needs a battery for his MacBook and I do not use my own MacBook battery, having changed to another laptop. My battery is fairly recent.

Is it safe to use my MacBook battery on his laptop? I cannot see any reason why it would not but thought I would check with a few knowledgeable users first.
Yes, however there are two versions of the MacBook battery, the Energy Star and the non-Energy Star that are incompatible with each other. So as long the pins look the same in his laptop you should be fine

Check out this post on super user for more details on the different pins of the Energy Star and non-Enery Star connections for the battery.

https://superuser.com/questions/186817/my-macbook-is-a-battery-denier