12V batteries, right?
Not necessarily. A typical 12V battery charges up to about 13.5V (12.5% over) or so when it's really charged. A 6V lead-acid battery charges up to 7.4V (23% over). That smaller ... View More12V batteries, right?
Not necessarily. A typical 12V battery charges up to about 13.5V (12.5% over) or so when it's really charged. A 6V lead-acid battery charges up to 7.4V (23% over). That smaller battery has the ability to overcharge by twice as much. I've seen some 12V batteries which will go as high as 14.5V but that's still less than the smaller 6V overage.
Okay... so what does that mean then?
I designed my own system at home (and suggest for customers) a 4 x 6V series battery bank. You generally call this "24V" but the reality is that you charge it up to 29.6V. And it's this overcharge that you use at night when the sun is down.
If you need more storage you then add four more 6V batteries, run them in series as well and then connect this new set in parallel with the original set of four. The overall voltage remains the same at 24V but the capacity now doubles.