Between John and I we've bought about ten of these. There is NO WAY these are a battery tender. They are just a regulator IC with a bit of circuitry to make the LED work right. They are advertised to put out 13.2 volts and will deliver at least .1 amp with fair regulation of the volts. The problem is that as delivered the voltage out varies from as low as 12.7 to as high as 14.8 volts and they are not temp compensated. The volts out can go up as much as .5-.7 volts when you take them out to the cold garage. This is not all bad because batteries themselves behave the same way with temp. changes, just not so much. It is fairly easy to pop open the little box and change a resistor or two as needed so make the output 13.2V for a slosh battery as used in trucks, motorhomes, KLRs and othe low-end vehicles. Similarly you can raise the voltage to 13.5-13.8V for use with AGM batteries. The little LED is a feature in that if the unit isn't plugged in the LED will light when you have the clamps correctly connected. It is a problem if you unplug the wall wart and don't disconnect a clamp. The LED and the sensing resistors for the regulator (a 7805 in my units) draw about .03 amps from you battery which sucks an amp-hr out of your battery every 30 hours or so. Even given the problems, if you take the time to get the voltage right they are a good deal at $5. If the voltage creeps up a bit they really don't deliver enough current to damage most batteries. If you are using them for an AGM battery though you need to be sure the volts out is high enough or they will actually discharge your battery. AND at least two of the units had a bad filter condenser (that's capcitor to you younger guys.) in the wall wart so I had to cut that open and replace a part. It was less hassle than returning them. I have the wheel balancer and it works fine.