[ainarssems]

After playing with solar sunroof to charge battery last year I did not have much hope for this charger but at £13.99 it was cheap enough to try it out.

So it arrived today, it says in specifications ratings at max power: power 2.4W, Voltage 17.5V, Current 138mA. I tried it on old, half empty but still usable battery in the garden with the panel pointing directly at sun. Open circuit voltage 23V, battery voltage 12.28V without charger connected, 12.3V with charger connected and slowly climbing, current 151mA, total power 1.85W. Put in the shade and current drops to 13mA.

So it's pretty much as I anticipated, it will not charge up flat battery, might just stop it from discharging during bright daylight sun but will not charge enough to make up for the charge lost during dark hours. Overall it will slow down discharge so your battery might last 1.5 months without driving instead of 1 month. To keep battery fully charged you would need 3 of these panels or 1 that is 3 times the size assuming it will be pointed directly towards sun.