Therefore topping up the battery charges to it's optimum and fullest potential becomes very important for me. I bought a 4.5W solar car battery charger (picture on the right) from DealExtreme to try out and regretted about it because it was under power and would take weeks to top up my battery to its fullest.It comes with a cigarette lighter adapter with an LED indicator when there is enough sunlight to charge the battery. But I discovered that the circuitry to power the LED pulls down the voltage so much that it left with not enough voltage (below 12V) to charge the battery.
I ended up connecting it directly to the battery terminals and later on added a PWM charge controller because I was worrying of over voltage as I measured 19+V open circuit from the solar panel.
As I mentioned, 4.5W is too small that it will take weeks to top up my battery. The battery status of my 10A PWM solar charge controller always shows red in the morning before I crank up my car engine. I ended up purchasing a few 10W semi-flexible poly-crystalline solar panels from eBay and here's a short video of the 10W panel with 10A PWM charge controller.
With this Solar car battery charger, I now have the peace of mind that my car battery will always be top up to its fullest potential and will prevent lead sulfate from building up on the battery plates which will shorten the life span of the battery.
I have also added 2 10W panels to bring the total wattage to 30W so that it can top up the battery everyday.
