[Boonga]

I have recently aquired a second hand DR 250 1990 bike.
I have two questions that I need help with.

1) The battery is flat and will not charge. The bike will run and all electrics function normally without it when the engine is running. Do I need to replace the battery at all and will operating the machine without it damage my electrical system.

2) The engine misfires at high RPM and under load. It is not consistant so I am guessing it is not an electrical problem. I have replaced the spark plug and have good spark. It has a Mikuni Vacuum slide carby fitted. I have cleaned and replaced all seals and tried various needle adjustments to no avail. Do these carbys have a problem area that I have missed? I realise it is a pretty big ask to fault find a bike over the internet but I was just wandering if this is a common fault with this model of bike.

Thankyou very much in advance.
Boonga