JohnC's approach is certainly cleaner - hitting requires lying on the road to reach the starter! Although, I never managed to get the in-gear-rocking approach to work. Whereas a good thwack!...
One last word on the battery - I've had a lot a replacements over the years due to various problems including just leaving it connected for months and not using the car. I used Unipart Samson ones which were guaranteed for the life of your car and managed to get at least one new replacement when the battery died.
Last time I tried to get a replacement (I'd been disconnecting the battery when not in use, so no negligence on my part this time!) the Express Factor wouldn't exchange it for a new Samson without going through a full warranty process. Trouble is, I needed a new one there and then. They did replace (free of charge) my Samson with a cheaper one that was the right size although I was a bit suspicious of the Ah rating. When I queried this, he produced a monster battery of the cheaper brand that wouldn't fit the battery tray, so I went with the 40Ah (or so) battery that did fit directly - and to be fair, he said any problems he'd swap it without any questions.
The point of this is that although this battery was kept topped up with a battery conditioner (which is excellent), a trip to Cheshire and one night away from a conditioning top-up was enough to trip me up at Warwick Services petrol station with all the engine bay fans still blowing after a blast down the M6/M40. When I tried to re-start the car with the fans running, there wasn't enough chuff left in the battery.
The owners handbook specifies 50Ah (at least, as far as I can remember) and I now know why.
After bump starting it by myself (pratically on the slip road when it fired up!
) and getting home, a quick hook up to the conditioner brought the battery back and it tested as strong and at max charge. No fault in the battery - other than it just didn't have enough capacity in Ah and CCA.
I've since replaced this with a Varta (which is apparently what's inside a Bosch) that has excellent Ah and CCA. After lots of research it seems that any battery that's easy to get and has the required capacity/power is physically too large for the GTA spec. Interestingly, my good old Unipart Samson was the right size and charge but these are expensive and trickier to source.
So, I bit the bullet and bought the Varta which has been excellent. The only down side is that I've had to slightly modify the battery tray. The results have been worth it, though, as I now have a battery that can cope with all the electrics that the GTA needs to run when it's hot and (dare I say it?!) wet.
My research (albeit web-based) for a battery the right physical size just isn't up to the job in a GTA - so make sure if you need a new one, that it's up to the job in terms of capacity/cold cranking/Ah etc.
Jon