How can I get a replacement rechargeable battery for my Sylvania SDVD 704-OB swivel-screen DVD player? And what is price? ... Original battery now holds charge for about 1 hour.

SOURCE: My Portable DVD Player Battery can't hold a charge

Rechargeable batteries can only be recharged so many times. They begin to slowly lose their capacity after about the first 5 charges until ultimately it won't hold a charge anymore. It appears that this is your problem. Look for a model number on the battery & do a Google search for it if you want to try & replace it. You might also find it is cheaper to buy a whole new DVD player than it is to buy a replacement battery.

SOURCE: I CHARGE BATTERY BUT IT WONT HOLD CHARGE

Rechargeable lithium batteries have a half-life of about three years. That means half of the capacity is gone is three years - another quarter in another three years. Replacement batteries can be found online. Even if your battery is not that old, this is the most likely reason for short run-life.
It is often possible to get the chemicals in the battery refilled by an online vendor. This is not only cheaper and makes the battery, literally "better than new", but is also easier on the environment.

SOURCE: Battery RB-04EB

found a site for this battery. store.audiovox.com the battery is $42.00 though.

SOURCE: what's the serial number for the Sdvd 7015 Sylvania portable DVD player

Check the back or lower part, serial numbers shoud be there. All electronic equipmente should have a serial