If it's running up to 14V the alternator's fine. 12.6V is a little low for a "fully charged" battery, I'd be looking for closer to 13.2V. If this is recurrent (ie it ALWAYS discharges when the bike's off) and you've checked your battery connections as Pat suggested, you either have a partial short someplace or a dodgy battery that'll accept a charge but won't hold it. If your volt meter's actually a multimeter (or if you have an ammeter handy) set it up to measure current leaving the battery when the bike's ignition is off. It should be nil current unless you have a clock or alarm (disconnect them and measure again). If you find a current, start unplugging things (start with the light bar) till it stops.
