Hi..
Bike is sitting for unknown period..
I charged battery all night...it now shows 11.84V..
I connect it to bike(K100RS 1988) and all electrical parts working fine but engine it doesnt turn good but slowly...
I must buy a new battery?
Can i connect my battery to my car battery or i will damage something?
Please advice.
Thanks

You MUST not try to start the bike with a low battery. I will result of burning the starter relay.
However, you can boost you K100 with you car battery and booster cables.
As soon as the engine is started, unplug the car battery.
This is safe!
Have you checked the level of electrolyte in your battery?
If the level is OK, I would say that the battery is shot and you need a new one.

As I posted in the other section it is sometimes possible to recover sulphted batteries but I fear CF may be right.
Regards,
K-BIKE