Can't tell if it's working or not

I installed it in October, so we're already getting less sunlight per day. I was hoping it would keep the battery topped off, but it's still draining down to about 60-70% every couple weeks, so I have to also use a plug-in charger. Maybe it will work better when there's more daylight. I do have it pointed directly at the southern sky for maximum exposure on the windshield with the suction cups.

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