Have you checked out the manual or their web site for this info?
Usually the internal batteries are Lithium and will either be the button type that you see in computers or will have flying leads that are soldered to the board. If this is the case, take care in soldering them in, as if you take too long or apply too much heat you will ruin the battery.
First place to start would be the manual or web site
In the manual it says to take it to your dealer and have them change the battery. But our problem is that the board was given to us about 8 years ago and we have no clue what dealer to go to if we have to. We just want to change the battery and get on with our studio recording.
here's a slight problem with that locator, I am in Canada. More specifically Vancouver BC. If you can find a dealer near here without having to cross the US border that will be most appreciated or just what type of battery it is.
Now I am going to say this with the following warning:
If you do not feel confident in your abilities or you do not have the authority to dismantle your board than do not read on.
OK - if you unscrew the back panel on the board you will probably be able to see the battery. From my experience, they usually make them easy to find/replace.
If I get a chance, I will have a look on the web for the manual and/or tech support. If they are available. I assume that you have already done this?
If not, do so. If nothing can be found, send an email to the Yamaha head office for the US/CAN. If there is an audio service centre close to you, call them and ask for their advice. After all, this board is 8 years old and well out of warranty, so you do not have to go to an authorised service centre. Especially for something like changing a battery. Was it a more specific problem, maybe.