Agree with what Steve has said about batteries but it is worth noting that warranties issued usually only cover what they consider to be the remaining life of the battery. I had a battery fail some time ago which was still under the 5 year waranty period, when I claimed I was told that I would only get back the remaining two years i.e. 40% of the original cost of the battery. It is worth investing in a good quality unit though, less likely to need the warranty.

Nich.