ABS light and misfire?

[Nero]

2 weeks ago, I replaced the battery with a new one. The old one was 5 years old.

Now, my new battery died. So I "helped" the S2 Avant starting.

While driving, sometimes the ABS light got lit, and I got a firm misfire. Than the ABS light is off again.

What could do this?

Is it the battery, whick seems to be very bad. Or is it a bad earthing? The battery and cables are connected firm, no problems with that.

I'm going to exchange the battery today, but I am very curious what the problem is?

[Fat Audi 80]

How did you "help" it start?

I understand there are potential issue with bump starting these cars. (According to the manual anyway...)

[Nero]

We pushed the car, and I have used cables. I know the manual's issue about cables.

I must say that it was very hot outside, something like 30 °C. I don't use the car much, so I might try it today. Much colder now.