Short answer: Contrary to some of the negative reviews speaking about "warping", "discharging your battery" and other such things, it works exactly as advertised. I drive the test vehicle only a handful of times per year, so it sits outside for months on end sometimes which is bad for batteries, they like to be topped off all the time due to their internal chemistry.Long answer: I'm an Electrical Engineer so I did a few basic tests, with the following findings and some recommendations:NOTES: DO NOT leave the panel plugged in when starting or driving, spikes in the line might cause damage to the circuitry. It could fail and then put a load on the battery in that case. NO test for weather/water resistance was conducted, I have yet to test it in the winter time, which is a more challenging time for it and batteries too. I'm optimistic it will work ok given what I've seen so far. I tested this resting on the dashboard (no suction cups, I wouldn't trust that ever), with clear view of the sky facing generally slightly east of North during mid-late August, near the Washington DC area using a cigarette lighter connection with the supplied adapter. (it's FUSED, and works with a NEGATIVE ground socket/system, i.e. most everything not vintage) Some people have said the cig cable polarity is backwards, but in order to work as a CHARGER, the + connects to + as it should! Btw, the BLUE LED does NOT adversely effect the performance, and need not be "disabled" as some have claimed. The numbers I'm reporting are all with the unit as delivered, no modifications were made.1) NO Battery discharge when dark (i.e., it doesn't drain your battery in the dark, or ever due to internal diode) Tested on the bench as well with a power supply and ammeter.2) NO WARPING of case in direct sun 8hrs/day mid latitude US East Coast in August. (measured CABIN peak temps up to 117 deg, low of 69F, dash probably hotter in direct sun). ABS plastic has a glass transition temp (i.e. warping) around 105C (221F) so IF it is actually ABS, no melting/warping seems possible at temps found in cars NOT on fire lol!3) For a HEALTHY battery, it MAINTAINS charge easily overcoming a parasitic drain in my vehicle of 9mA or (0.009Amps), and still puts a NET 44mA (0.044Amps) charging current INTO the battery in direct noon sun, and a NET positive charge current (in clouds/overcast), albeit only 7.3mA. In only 1 sunny day (and overnight) my new battery @ 12.34v went to 12.55v from this device. This is because it is a HEALTHY battery. The max open circuit voltage of the charger I measured around 22v but it can only deliver 1.5W max so you aren't going to hurt the battery with such low currents, and at best charging currents are only present up to about a 1/3 the time during a 24 hr period I'd estimate.NOTE: A dead/failing battery cannot be rescued by this or any charging device, and my prior failed battery at 12.24v (after 2 day commercial charge from "dead") with this same device under same summer conditions in 2 days went down to 12.01v and failed to turn over the engine! After the attempt it was down to 11.5v, clearly no good.I think this is suited as a MAINTAINER, don't bother thinking this will "charge" a vehicle battery. I drive that vehicle very very rarely, so this will keep the battery ready to go without having to periodically start it every few weeks to charge it up.Temperature and time will reduce the efficiency of the panel, but there is a 4x margin in my case (with a 9mA parasitic drain, which is quite small). If your car has a lot of electronic features, security systems etc, your parasitic drain could be more than this can even put out. In that case you would need a bigger higher power panel (this is only 1.5W).To measure the parasitic drain: with all vehicle doors shut, pull the main battery fuse and put an ammeter there, since it will measure absolutely everything, using any other fuse will only get a subset of what your battery drain is. Start with the maximum scale (typically 10A) to be safe, switch to smaller scales once you know the range. Let the initial connection settle since there will be a surge for a bit as all the electronics initialize and settle into a steady state. My vehicle settled in about 5 seconds (an after market CD player self test used 250mA during that 5 seconds)In principle, some sensors and other fancy stuff could spike some current periodically, but this couldn't be known without a logging ammeter. In all likelihood it won't boost the average drain in any significant way from your measured steady state.
