My old car battery died because I leave it parked too long. I replaced with new battery and this time hooked a solar trickle charger to it to keep it from discharging. (it's parked in public space)
I left the car parked for 6 days, I measured with multimeter before and after the battery. Before 6 days, battery rested at 12:45, when turning ignition on it goes to 10:49, engine nrunning at 14:22. After 6 days battery rested at 11:94, turning ignition on has it rise to 9:96, when engine is running it rises to 13:51 and increasing higher.
The car is small and has a small sized battery.
The solar charger itself in that parking spot which has okay clear sunlight not straight at the sun, when I measure it during day it reads 13. Manual for it says it should be 15 minimum at full sunlight. What I noticed is in places where it's really sunny the solar charger turns on the digital clock even when car is off. So clearly the car receives the power from the charger. But in my usual parking spot that measures 13 with multimeter, doesn't do that.
Edit, what's this red blinking light behind radio?