Determining battery capacity?

[GigaBrick]

The battery life meter on my Rockbox seems to be pretty inaccurate, and after reading up about the Battery Capacity setting, I'm not sure which value I need to set it as.  I'm still using the factory default battery in my Toshiba Gigabeat F40, but I can't find any information on what the default mAh on it is.

However, looking at most of the replacements that I can purchase for it, it seems that it is 1000 mAh.  Is this a good estimation to make based on what power replacement batteries offer, or is it more likely the factory default battery is rated at less?

[Llorean]

If you still have the original battery, it's probably effectively less than its original value anyway due to age.