It won't matter as it will stop sucking sunlight.
Yes, the weight of batteries does increase when they are fully charged due to the additional chemical energy stored in the battery.
Yes, batteries are typically heavier when they are fully charged because they contain more energy stored in the form of chemical reactions.
A fully charged 12 volt automotive battery should have 12.68 volts.
Not fully, but these days come more than half charged, yes.
No
12.6 volts when fully charged.
12.6 volts when fully charged.
12.8 - 12.9 volts is a fully charged battery
Yes, it should shut off when the batteries are fully charged. If not it is either a very old charger or it is defective. You do not want to overcharge the batteries so use a charger that shuts off automatically.
Virtually all automotive batteries nowadays are nominal " 12V " batteries, but will measure up to 13.6V when fully charged.
No --the slides will open with fully charged batteries.
That means it dosent have to be charged anymoreWhen you start to charge and the red light flashes for a while, then it changes from red to green alternate flashing this means that the actual batteries doing the charging are not fully charged. Either buy new batteries or make sure you charging batteries are fully charged before you attempt to charge it