My house entered full power saving mode with fall. Lantern light and all devices shutdown at bedtime.
But, it felt early to need to do this. Comparing with my logbook for last year, the batteries were indeed doing much worse.
I had added a couple of new batteries to the bank last winter, and they seemed to have helped at the time, although it's difficult to tell when you have a couple of good batteries amoung a dozen failing ones.
The bank was set up like this:
+---- house ---- | | +( 6v )-+( 6v )- | | +( 6v )-+( 6v )- | | +( 6v )-+( 6v )- | | +( 6v )-+( 6v )- | | +( 6v )-+( 6v )- | | +( new 12v )- | | +( new 12v )-
Tried as an experiement disconnecting all the bridges between the old 6v battery pairs. I expected this would mean only the new 12v ones would be in the circuit, and so I could see how well they powered the house. Instead, making this change left the house without any power at all!
On a hunch, I then reconnected one bridge, like this -- and power was restored.
+---- house ---- | | +( 6v )-+( 6v )- | | +( 6v ) ( 6v )- | | +( 6v ) ( 6v )- | | +( 6v ) ( 6v )- | | +( 6v ) ( 6v )- | | +( new 12v )- | | +( new 12v )-
My best guess of what's going on is that the wires forming the positive and negative rails are not making good connections (due to corrosion, rust, broken wires etc), and so batteries further down are providing less and less power. The new 12v ones may not have been able to push power up to the house at all.
(Or, perhaps having partially dead batteries hanging half-connected off the circuit has some effect that my meager electronics knowledge can't account for.)
So got longer cables to connect the new batteries directly to the house, bypassing all the old stuff. That's working great -- house power never dropped below 11.9v last night, vs 11.1v the night before.
The old battery bank might still be able to provide another day or so of power in a pinch, so I am going to keep them in there for now, but if I don't use them at all this winter I'll be recycling them. Astounding that those batteries were in use for 20 years.