12voltpower

A Battery will recover a little over night when no longer in use! sometimes even enough to start a car when flat the day before.

Cheers

Might also have something to do with lower overnight temperatures.

Johno,

A 12V battery actually has an internal voltage of about 12.6V, or a bit higher. This voltage is determined by the chemistry of the particular battery.

When current is drawn from the battery, losses occur both within the battery and in the external wiring, so the measured voltage will be lower than the nominal internal voltage. This effect is also present for some time after the current flow ceases. In the morning after the system has had time to equalise with no loading overnight your measurement will be very close to the actual internal battery voltage. So..... you aren't actually seeing a higher voltage in the morning -- it's just that you saw a lower voltage the night before when the system was in use! (Of course if you have some solar panels feeding in, you'll see a higher voltage in daylight than you will at night too, for obvious reasons!)

Cheers

John