The battery is hard soldered to motherboard.
1) Ignore the message, unless you can find away to disable the message report from the bios which I doubt there's any. P.B. went to solder the unit the board to cut cost.
2) Get someone to replace the battery with battery holder unless you can do it yourself.
There is really not much on the bios that require re-configuring if there's a power failure except time and date. It's not crucial if you can't replace the battery.