Question about Battery Meter and Charge Options on L521X

The Dell Battery Meter (probabaly from the newest Quickset) has two tabs saying Desktop Mode and Longevity Mode. However I do not understand how they work.
First, Desktop Mode, if enabled, says 'Battery will only charge between 50 and 100%'. What does this mean? The Battery will not charge below 50%? Or it will not charge fully, but randomly charge to a percent between 50 and 100%? What will be that percent?
Second, Longevity Mode, the whole tab is disabled, I can't select any option.
Thanks for any help.

 

so is there any experience sharing about this battery meter application?

 

I just got this laptop with windows 8 and these battery options aren't as straight forward as I'd like it to be. It seems both tabs do almost the same thing except both won't charge at a certain level but it seems having both on will conflict.

I know on the Dell 15z there was a dell battery meter option where it allowed you to disable the battery at any level. I was really hoping to get an answer to this as internal batteries are a pain in the and I'd like to think that we would all like to have the battery live a little longer even though batteries these days are a lot 'smarter'.

obviously, the battery doesn't charge at 100 percent but it'd be great to be able to disable the charging when plugged in at any level . Is this still possible as it was with the Dell 15z?

I'm also finding with this laptop in comparison to my 15z that after turning it off for a day, I'm finding the l521x (windows 8) has had at least 5-6 percent battery drain in comparison to the 15z (windows 7) where there's no change. anyone else?