I worked at Staples (last day was 3 weeks ago) and yes, Staples does cover the battery with no exceptions. That's where the warranty comes into play. The battery is most of the cost and the rest is a just in case factor should something go wrong. One thing that we always saw come in was broken power inputs. The adapter came right off the motherboard and sometimes in that case, the entire motherboard needs to be replaced, which is a good $300.
It's really all a matter of if you want to feel safe and secure with your purchase. Another good thing at Staples, and this is an awesome deciding factor, is that you can get a COMPLETE REFUND of your Extended Service Plan before the manufacturer warranty is up. So say your laptop is working amazingly 11 months in, personally I would probably get a refund on that $150 or whatever. Staples will also refund your ESP after the manufacturer warranty by prorating it. So, you spent one year of the extra two years, you'll get $75 back or whatever.
Remember that Staples' 2 year plan covers the manufacturer warranty, AND THEN Staples' 2 year ESP kicks in.
Staples also deals with their service plans themselves, rather than outsourcing like what Future Shop and Best Buy do. In Ontario, Staples has a service depot right in Sarnia, so it's not like it has to go a long way to get your laptop fixed. Not only that, but they are certified techs for many different manufacturers.
Anyway, I hope this helps.