This item works great for the most part. I gave it 4 stars instead of 5 for a couple reasons.
1) It will not send ANY charge into a fully discharged battery (even if the battery still works), so you have to jump it before using this device on it.
2) The charge level on it seems to bounce around a lot (it will tell me a battery that was fully discharged, got jumped, and then is charging with this is at 90% charged and a few hours later it will say it is 70% charged). This % fluctuation happened on 3 different batteries that I used the device on. This isn't too big a problem though since it will keep charging if you leave the device on and plugged in, and it does seem to stop when the device is at full battery (you just can't use the % charge for any indication as to how close it is to having a full charge).
For the price I paid for this item though, these are rather minor complaints and this item is excellent value and does the job well (but if you have a fully discharged battery and no vehicle to jump it you might want to look for another device-plenty of them on the market can do this).