As the driver of an electric car that is reliant on a lithium-ion battery for motive power I don't believe Li-ion technology is inherently rubbish, however it does require a sophisticated BMS (battery management system) to ensure safe, reliable, and durable operation. I doubt that the simple charging circuits on a 12 year old car will have that capability, so it seems to me that to fit a 12 volt Li-ion battery to the A3 is both wastefully expensive and a retrograde step in terms of performance. A plain lead-acid battery would do the job adequately.