I've had some trouble starting my mini.

It doesn't seem to have enough power to crank the starter motor.

I have started it with jumper leads connected from another car.

I get 12.3V from positive solenoid terminal to earth, and the same from the car body to the positive battery terminal. If I arc the solenoid terminals I get only weak sparks whereas usually it will try to weld the pliers to the terminals.

Headlight switch does not seem to have enough power to trip the relays that I wired up ( I can hear them buzzing).

Usually when a battery is dieing it will crank slower and slower until there is nothing left. I'm confused as to why it seemingly lost power all of a sudden. Is there something else going on here, or do I just go and buy a new battery?

How many times have you shorted the battery to itself? Maybe that's what's killed it.
Buy a new one, dont test it by shorting it......incase you didnt know, there's a petrol tank 2 feet to the left.

Thanks for your reply.

yeah, I'm not a pro with a multimeter..

do you mean I'm shorting the battery by testing it with the multimeter? I don't get sparks when using it.

Only sparks I get is when I arc the solenoid, which is a few more feet away from the tank...

I've missread that, thought you were testing the battery by shorting it to itself......which I have seen done before!

You're using the multimeter just fine, its the shorting which you should avoid.

If you have fully charged your battery off the jumper leads for a good long period, you should be looking at 13.8 volts across the battery terminals. To get a charged battery voltage of only 12.3 volts does not seem to be that much different from 13.8, but it makes a huge difference to the cranking power of the battery. It's just he way they're made up.

If you have charged the battery and this is the best you can get, then its time to get a new one.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Thanks guys. I'll see if I can charge it up and see how it goes.

Thanks for your help!

make sure all connections are clean and corrosion free