These are some great Tips from Mr. Verse from The Powered By Danger Forums!  He originally wrote this for a SK3 but it applies to the Sidekick LX and the Sidekick Slide as well.  Hopefully, these tips will help you get better battery life!

He  “trained” his original SK3’s battery to last about 18-20 hours with a 4 hour charge.
This trick really only works within the first week of use. If you’ve used the device for 2 months already, this won’t help as much (but it’ll still help). Keep in mind, when I say “train the battery,” I mean RECALIBRATING THE BATTERY METER:

A) I cannot stress enough that the initial charge out the box is crucial. Instructions state you should charge the device 6-8 hours upon initial start up. Most people are so geeked by getting the device that they yank it off the charger 3-4 hours later so they can go out and floss their sidekick. HUGE mistake. Despite evey urge to do so, let it charge at least 6 hours out the box.

B) Now, for the next couple of days try and let your device totally drain out it’s battery before you charge it again. I’ve had a couple nights where I come back from work with the device already dead (Sucks for my commute, but well worth it in the long run). When you finally do plug it in, make sure it charges 4-5 hours minimum before you remove it. I usually leave them plugged in overnight…

C) You’ll begin to notice an improvement in your battery life. Your device now has new “baselines” for when it’s full and when it’s not. Keep it up for another day or so (but don’t waste an entire week doing it) and then you’re set. Sometimes I would bypass the old automatic cutoff for charging by charging it while off just to make sure I “topped it off” (NOT reccomended for consistent charging, tho’).

So that’s what I did, and have done for every SK device since the CSK. My replacement now lasts me 18+ hours with heavy browsing, IMing, texting, and 1.5 hours of MP3 usage(commute). By the time I walk in my door, I usually have 1 bar left or the battery warning (which now lasts me about 30 minutes)…

Many have said I’m lying, and that it’s impossible to “train” a lithium ion battery, but if you are consistant out the box, you can definitely recalibrate the battery meter to peak accuracy… Heck, my old SK2 used to last me 2 days solid (at least) between charges.

See more of his battery training and performance tips here.