OK, so now I've actually finished the decking - screwing in the final screw about 30 mins ago. Whilst we were out earlier Kat and I did some maths, and realised that we used about 700 screws in total for the decking. I also discovered in this project that of my two drill driver batteries one is in much better shape than the other. I counted screws from a full charge, and one battery managed about 70, and the other just under 30. I have no idea if there is anything I can do to restore the weaker battery. And I would guess that both are down from their new condition.
It's projects like this that help me really see the difference between a very cheap tool (which would probably have driven me mad), my moderately priced (it was about £120 new) and the very expensive tools that go up to a few hundred pounds. That difference is amp hours. (OK, so there are other factors but this one is a biggy.) A great deal of the end of the project was gated on how quickly I could get screws in. That meant I spent a lot of time waiting for batteries to charge. Even with two, 2 hour charge batteries. Only one charger meant that I quickly caught up using up both batteries, but only being able to have one of them recharging.
That said - for the money I paid I have a very good tool. I'm sure I'd have had much more frustration and difficulty with a cheaper tool with not enough torque, etc. The question is really: how often am I likely to need to put 700 screws in? The temptation to use this as justification to buy a new drill driver, with more batteries, and more chargers is great. I'm even more tempted to buy a third battery and second charger for the one I have.
Yet I have come through this project, which was very demanding on this tool. And it really wasn't that bad. When the weather was hot and I was sweltering in the heat, the excuse to take a break and have a drink in the cool was good.
So yeah, if I was going to go into business putting together decking for people, I'd spend some serious money to make sure I had a tool that didn't hold up the job. But for me, I think my little Bosch GSR 12V 'professional' has proved that it was well worth the money, and good enough for some serious DIY projects.