Planned obsolescence

I hate the thought of buying a new computer just because the battery on this one no longer holds a charge. On the other hand, I also hate the thought of buying a new battery only to have the computer in general crash and burn three months from now. And what I really hate is the thought of buying a new battery, only to have the battery stop working three months from now, which seems to be what users on the Dell website suggest will happen. (Well, they say nine months, but I still expect better from a $156 battery.) And really I don't need something that lasts for four hours in any case; I just need something that won't shut off completely if my plug falls out.