I am an avid DIYer, as well as someone who works with a high-end tool company that ends with -on.
The discussion (debate, argument, yelling match) about why someone should pay big bucks for the best tools comes up on a regular basis.
The best answer is that if your depending on your tools for your job, all day long, day after day, you need the best.
If you are just going to use a tool every now and then, cheaper is ok.
Some of the impact sockets from harbor freight are actually dangerous because the metal is too brittle?not weak, brittle. You want a tiny amount of give in the metal if you are stressing it out. Otherwise you could get into a shrapnel situation.
As far as batteries in an RV, I think they fall into the "depending on it all day, every day" category so I wouldn't skimp with batteries. A high-quality battery is totally worth the price. And I am totally jazzed about the "Genius" line of battery trickle chargers for stored batteries. Fantastic products.