My first thought would be to get a laptop that has good battery life and then get a one or two spares. I could see why you might just want to get a charger if the battery life was only 2 hours per charge, but things aren't that bad anymore unless you're gaming or something.
For example the Dell latitude e6430 lasts for 5+ hours of surfing on wireless in this review (»www.notebookcheck.net/Review-Del···0.0.html
That's with a 6-cell, so with the 9-cell should last about 8 hours.
So with a 6 and a 9, or a couple of 9's, you should be able to get at least 12 or even 15+ hours out of it.
The only downside is that you would need to remember to charge them all up in the evening to get ready for the next day. They charge pretty quickly though, i think the 6-cell in my e6410 can fully charge in about 90 minutes, so you would just need to remember to plug it in after work and then swap the batteries before bed.
The other sacrifice you are making here is that the e6430 is a relatively small laptop. If you want a bigger 15" 1080p unit like the e6530 the battery life is not going to be as good, probably 3.5-4 hours on a 6-cell instead of 5. At that point you are going to need at least 3 batteries or a charger like you describe.
I also see that you can get an additional 3-cell for the optical bay of the e6x30 line. Not sure it's worth the money but it might be if getting a long time on a single charge (with 9+3 for 12 cells you could get 10+ hours with the e6430!) is important to you. GIven that you say there is some time to charge up at lunch this could do it for you with none of the swapping hassle.