I was thinking about getting a Dyson but the price was crazy so I took a chance with a cheapo Hoover 5221 on sale for about $129 + another $50 for the better power head. I assumed it wouldn't be much cop and more trouble than it was worth at that price but it does a good job and i've never run the battery out. The capacity for dust etc isn't that big but it's easy enough to take apart and clean so it's not a big deal.
Try taking yours outside and using a blower to clean it. That's so much faster and easier.
