wrote:
According to the Battery Tender folks, the health of the battery can
be determined by measuring the voltage across the terminals after the
battery has been at rest for about 24 hrs. A full 100% charged battery
will show 12.9 volts, and a fully discharged one will show 11.4 volts.

IMHO, the 12.9 V figure is a little high. I usually expect and see about
12.60 - 12.65 V for a fully charged flooded lead-acid starting battery.
For whatever it might be worth,
http://www.uuhome.de/william.darden/carfaq.htm has about the same
numbers.

I've used the Battery Tender chargers and they work well, but I am also
not surprised that a manufacturer of battery chargers gives a figure for
"fully charged" that probably makes many batteries tend to look
discharged. Never ask a barber if you need a haircut.

Disclaimer: This is based on experience with flooded and VRLA/AGM
batteries for starting and traction on ground vehicles. I don't have
an A&P; I don't even have a TG&Y. I don't get money or other
consideration from any of the companies mentioned.

Matt Roberds