That was me.
Yes I did get it. £20 from a caravan and camping shop! The first weekend I got it, my battery was completely dead as the proverbial Dodo. I jump started it, gave my car a brief run, plugged in the solar panel and left it another week. The following week, I tried it, the battery gave a half hearted attempt, but was still pretty flat and didn't have quite enough to turn the engine over.
However, it had been a very cold week, the battery hadn't really been charged much and I'd left the alarm on, which I know does drain the battery if the car is not used. So, I jumped started it again, gave the car a good run round all weekend and left the alarm turned off and since then it's been starting fine every weekend, even though it doesn't get driven all week and the weather is still pretty cold. So, I'm guessing, as long as your battery has some charge in the first place and you haven't got any battery sapping alarms on, the solar panel is probably doing just enough to prevent it going flat.