What's the best portable jump starter?

I'm thinking of buying a small, portable jump starter to keep in the glovebox just in case I get a flat battery. Is there a specific model or brand that you'd suggest looking at and how much should I pay?

Can you recommend a good, small jump start pack?

I have read quite a few forum posts about jump starting modern cars (or not) using jump leads, and the (various) procedures to do it (or not), and am somewhat confused. Some say that using jump leads on...

Will aftermarket accessories invalidate my warranty?

I recently bought a brand new MINI Cooper. It doesn't have sat nav as standard so I bought the Mini Click and Drive base system from a company selling genuine Mini accessories. I also wanted to have a...