I bought this primarily for the batteries. (which seem to work just fine in my MyTouch 4G Slide) The charger was almost an afterthought. When I opened the box, I was initially rather disappointed with the charger. I was familiar with battery-specific charging docks. They're idiot proof - snap the battery in and walk away for an hour. This one is pretty generic. You have to set it up for each battery by moving the little contacts around each time, and the battery stuck out over the right side even with the contacts pushed all the way to the left. I was kinda peeved that they wouldn't go to the trouble to put a battery-specific charger in the box. What I didn't immediately realize was how much usage I would get from this MULTIPURPOSE charger.
Two days after I had added it to my charging station, I found myself with a stack of dead, spare batteries for another phone, and only a single dock for that battery type. After charging one battery from the stack, I noticed the empty dock and it clicked: Stick the old battery in the new dock!
This thing is great!
The instructions are pretty simple. Line up the contacts with the + and - terminals labeled on the battery. Don't worry about polarity, the circuitry sorts that out for you. (I've stuck the battery in upside down, no problems) The third tab is to hold the other corner of the battery in the proper spot so that the battery doesn't twist in the charger. The deck is spring loaded to clamp the battery securely to the contacts, and it spins around to handle longer batteries. It has an indicator light that appears to glow red once you get the battery installed properly, and switches to blue once it is fully charged.
Now, I still want a dock specifically for this battery type, so I can drop a battery into the charger without having to fumble around with the pins and the deck, but every time I find myself with a stack of dead batteries for whatever phone/camera/GPS Puck/other random device I'm working with, I'm glad I have this charger to pick up the slack!
In addition to charging nearly any small-device battery, the charger has a USB port on the side, so if you have the USB cable for your phone, you can charge two batteries simultaneously.
The rated capacity of these batteries is roughly 25% greater than the rated capacity of the OEM battery. These batteries are rated at 1900mAh; the stock battery for my phone (BG58100) is 1520mAh. BUT, you have to remember that all lithium ion batteries lose capacity over time, usually about 10% to 15% of the rated capacity per year. A two-year-old, 1520mAh OEM battery may have an actual capacity around 1000mAh, or even less if it's been abused. Thus, these new cells can easily have anywhere from 25% to 250% greater capacity than your current battery. The older your current battery, the greater an improvement these new batteries will give you.
ANY lithium ion battery, be it OEM or aftermarket, can be damaged and cause the problems people are talking about. Lithium Ion batteries can enter a condition called "thermal runaway", where they rapidly self destruct. Virtually all lithium ion batteries have protective circuitry within the cell to cut off charge/discharge and prevent this from happening. The commentator who talked about the battery damaging his SIM card; that defective battery would have done the same thing on the included charger. The chances of this actually happening are on par with winning the lottery. If you're worried about it (and even as rare as it is, who wouldn't be after reading that review?) I suggest that the first few charges be done on the included charger, just to "proof" the cells. Pop one in your phone, run it until it dies, remove it from the phone and put it on the charger. If after two or three cycles the battery hasn't melted down, it will be safe to charge within your phone.