Will this unit regulate charging, so as to avoid over-charging a battery?

So a lot of misinformation here... this unit comes with a blocking diode built in to the unit (I have had one of these plugged into by van for about 10 years). This blocking diode prevents the car from supplying current into the panel (like at night), which would result in slow discharge of your car battery. You can leave this plugged in all the time (like for 10 years). The person talking about the Schottky barrier diode has it wrong. This type of diode has a lower forward drop voltage (less than half a traditional silicon diode). And you DON'T put it between the two terminals... in one direction it will short your panel and car battery (blow the fuse and probably fry the diode), if you put in the other direction it does NOTHING... it is in reverse bias, and essentially no current flows. If you decide to put it in series with the charger, you will reduce the available charging voltage (and therefore the available current) by about 0.3 volts. The internal blocking diode is already doing this job. If there is someone out there that has the problem of discharging the car batter overnight, you either have a bad battery or your solar panel blocking diode is shorted (not working).

I don't understand what good it is in lighter socket if car must be running. When running, battery charges anyway! What am I missing?

You're right. MOST cars don't power the cigarette lighter unless the key is on. So if the key is off your solar battery is not connected. That's why they give you battery clips so you can clip the PVP (PhotoVoltaic Panel) directly to the battery. You could hard wire a socket directly to the battery if you like. GO to a junk yard and scrap out an old lighter port from an older car and wire it in. Since this panel is a mere 300 mA (0.3 amps) you don't need heavy gauge wire. But you DO need to be sure you don't short out the wire on some sharp metal surface.

Why would you use an 18V charger for a 12V battery. It seems to me this would be too much voltage.

Solar panels can put out any voltage, up to some maximum "open circuit voltage". If you put the panel in the sun, and measured the voltage across the leads without connecting it to anything, you would measure 18v, which is the open circuit voltage.Solar panels also have some voltage at which they will generate maximum power, this is the "Max Power Point", hopefully this is about 12v for this panel.The solar panel will match the voltage of any battery that you connect it to, but if the battery voltage is above the "open circuit voltage" (18v), it will not generate any electricity, and will not charge the battery.Ignore the other answers here, they are not accurate.

Manufacturer	ALLPOWERS
Brand	ALLPOWERS
Item Weight	11.4 ounces
Product Dimensions	12.6 x 5 x 0.12 inches
Item model number	AP-18V5W
Is Discontinued By Manufacturer	No
Manufacturer Part Number	AP-18V5W
Special Features	Portable
Voltage	12 Volts
Wattage	5 watts

ALLPOWERS 18V 12V 5W Portable Solar Panel Car Boat Power Solar Panel Battery Charger Maintainer for Automotive Motorcycle Tractor Boat RV Batteries

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