Don't recall having any battery cover issues with either of my 4 speed Bullets. The 350 did seem to have an unhealthy appetite for rectifier / regulators, though - the original Newtronics unit failed on the way home from collecting it & the replacement (Sparx IIRC) went while on holiday in Germany. This was changed under warranty. I ran for quite a while with just a bridge rectifier and no regulator - with the headlight on & speed kept to around 50 in top it didn't overcharge. The 350 had a standard single phase alternator, whereas the later 500 had the oddball AC / DC split arrangement.