Originally Posted by rnath
I have used this cheap Harbor Freight $9.99 unit for the last 5 years when I put my Porsche in winter storage. Works fine. The battery in the vehicle has stayed charged over the winter and no problems starting the vehicle in the spring.
Automatic Battery Charger - 12V
There is a difference. The battery tender will charge at a high enough
voltage to create some minor bubbling. This keeps the electrolyte mixed and
greatly cuts down on sulfide build up.
The harbor freight one does not do this.
Also the battery tender turns on and off as needed to maintain full charge.
The cheap one just stays on at a slightly lower voltage all the time.
This isn't the optimal way to maintain/preserve your batterie$.