On Jan 30, 11:43 pm, wrote:
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.htmhas 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

Thanks for the resource, it has a lot of detailed information. They
state the following:

"Depending on the plate chemistry, the Open Circuit Voltage can
range from 12.6 to 13.1 for fully charged wet "Maintenance Free" (Ca/
Ca) batteries and tend to be higher in deep cycle than in car (or
starting) batteries. "

This goes with what little I had heard about aircarft vs car
batteries, which is that aircraft batteries have a slightly higher
voltage than car batteries. Seems that it depends on the type of
battery one has, so the 12.9 is maybe an absolute maximum. I don't
know for sure. I'll just keep reading.

Regards,
Bud