Here is the description of the product from the Harbor Freight web site:
This lightweight 12v battery charger lets you skip the hassle of recharging a battery by maintaining the charge in your car battery. The automatic battery float charger features an automatic safety shut off and copper battery clamps for better conduction. Lightweight and easily stored for quick access, this 12v battery charger is a must-have safety precaution for battery maintenance while traveling.
- Prevent battery self-discharge while maintaining the life of 12 volt rechargeable batteries
- Floating circuit maintains a full charge without overcharging
- Simple to use - just connect and plug in
- Automatic safety shutoff
This sounds like a fantastic deal for a useful product. The battery on my GL1100 had a tendency to run down over the course of a week and a half or so due to parasite draw of clocks and other electrical items. On top of this, I was going through batteries on my GL1100 about once a year. I figured this would fix the discharge problem and keep my battery in top shape, hopefully making it last longer. I also had another spare battery sitting in my garage that I wanted to keep charged as well, so I bought two of these inexpensive chargers.
I hooked up the chargers to my batteries and plugged them in. They lit up red, indicating that they were powered up and charging.
A couple of days later, I wanted to take my GL1100 out for a ride. I noticed the voltmeter on the bike showed 14.6 volts, indicating the charger was actively charging the battery. I was a bit concerned about this high voltage, which is above the gassing voltage for lead acid cells. I disconnected the charger and it dropped down to 12.6 volts, showing a full charge. I switched the ignition on, and the headlight came on - a bit dimly, I thought. I hit the starter, and CLICK. The headlight turned off. I hit the starter again, nothing. Looking at my voltmeter, the battery voltage was around 8 volts. Uh oh.
I hooked up my normal battery charger to the battery, let it bring the charge back up to 12.6 volts (which took about half an hour). I tried again, with the same results. I had seen this before: this battery was toast.
With fear rising in me, I checked the other battery that I had hooked up to a Harbor Freight charger. It too had been destroyed. Over $200 in motorcycle batteries destroyed over the course of a couple of days by cheap Harbor Freight chargers.
I threw both chargers in the garbage and went out to buy a couple of new batteries. While these chargers are cheap, it is false economy. They obviously do not do what they purport to do. Instead, they overcharge, sulfate and corrode the plates inside batteries, quickly destroying them. I have no idea how they actually sell these things - perhaps using them as a slow charger on a battery that is very low might work, but leaving it connected to a battery as a float charger (as the instructions tell you to) will quickly destroy the battery.
I cannot recommend this charger in any way. Instead, buy the Battery Tender Jr., which actually will keep a battery in top condition when left connected 24/7, and genuinely extends the life of the battery.