8W Mono Crystlline

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.

Very durable had for several years. They work great keep the battery always fresh just have to clean panel occasionally.easy to set up

Seems to work fine, putting almost 15 volts out measured at the cable end. Mounted inside my windshield with truck facing early morning sun, it brought a battery at 12.1v up to 12.5 v. Sun lasts about four hours before going over the top of the truck. So about four more hours of shade with bright sky light only on the panel. Only issue is there are two batteries on my diesel Ram pickup and the other (passenger side) battery is not getting any voltage. I am charging through the power port. Looks like I have to use the alligator clips on that one and keep both charged by moving the clips to the other battery every day or so. It would be nice to have a splitter so I could plug into the power port and have another wire long enough to go past the door moulding and into the engine compartment to the second battery. Or a splitter with two sets of clips, each long enough to reach the batteries. Not use the power port. One wire could be longer than the other because I mount the panel on the lower driver side of the windshield.I will experiment by letting the batteries go down a bit and hook up the charger clips to the passenger side battery and see if the voltage reaches the driver side battery too. I don't know how these batteries are connected.The suction cups are easy to lose. They are not very secure, especially if the panel is mounted vertically. Be careful if you move the panel a lot.

Works great so far. Last one lasted 5 years. I have a work vehicle, so i don't drive my personal one very often.

There are some reviews that indicate this 1.5W model will keep a full size car battery topped off. Maybe if it is in direct sun, every day without fail, it might. But not every day is sunny, and unless you are parked in an open field, you won't be getting sunlight all day. I tested with voltmeter and if the day is very sunny the battery will have same output, but a series of cloudy days, the output will decrease and it doesn't have enough power to bring the battery back up.Further research shows you want a 10-20W trickle charger to keep an unused car battery topped off. Nothing wrong with this product, but they shouldn't show a picture of a car battery and give a car accessory power adapter. This is probably useful for smaller battery that powers security system.

Keeps all my car batteries nicely maintained, saves fuel not having to run to charge.

This will not recharge a dead battery. It just isn’t meant for that. What it will do though is keep your healthy battery from draining to dead while the vehicle is not in use. I found the suction cups are 100% trash and shouldn’t be trusted one bit. Just use a sun shade and prop the panel up against it between the glass and the shade directed towards the sun (don’t be dumb). It really works, I have used it for 3 weeks now and started the truck it’s hooked up to last night for the first time since 3 weeks ago. The cables and +\- terminals could be much better quality as well. Overall it works and just know you get what you pay for. There are definitely better higher quality products out there. If your on a budget this ones just fine. Can’t say much about it being in the elements though, I keep it in the cab of the truck. Update.. the plastic case around the glass is starting to warp from the sun. It is still working but it’s starting to twist and separate and the seam. Final update, still working just fine as of may 2023.