Yoou can't recharge it, it gets replaced. Take a look at <http://www.ifixit.com/Guide/Repair/Installing-MacBook-Core-Duo-PRAM-Battery/297/1> for the one on a Core Duo, or ask your friendly Mac vendor.
Hope this solves your problem.
AlanD
On 13 Jan 2011, at 18:51, Žorvaršur Davķšsson wrote:
> On 13.01.2011, at 07:49, Michael Logue wrote:
>
>> Sounds to me that your pram battery is low.
>
> Excuse my ignorance, but how can I charge the pram battery? Is that some kind of extra battery?
>
> According to the battery status in the menu bar the battery is fully charged and has never gone below 95%.
>
> I have just learned that one must calibrate the battery of a portable computer.
>
>
> Žorvaršur
> OS X 10.6.5
> MacBook Pro 17