Regarding the 5ah DeWalt 20V Max batteries, they do indeed offer what might appear to be a considerable upgrade in the runtime department. But that upgrade does come with a caveat, in that they ...

The DeWalt 20V Max 4Ah Lithium Ion Battery is on sale for only $51, which is a whopping 70% off the original $169 price tag.

Per DeWalt, the 20V Max batteries power devices use a brushed motor and are available in 3ah, 4ah, and 5ah models, which theoretically run for 3 hours, 4 hours and 5 hours at a stretch ...