For those having problems with batteries - here's the adapter information (so you don't have to buy it from the manufacturer for about $80):

AC-to-DC power adapter; 6V, 800mA; Radio Shack: 273-1766

Adaptaplug "M" at Radio Shack; 5.5mm O.D.; 2.1mm I.D.; Radio Shack: 273-171

It cost me about $24 for this and it's well worth it! Love the bike!