<VV> Battery float chargers

[Craig Nicol]

Last week I wrote: "I just checked the open-circuit voltage of one of my HF
maintainers and it's only 13.3; I'll hook it up and give you a full report
later"

Today, Padgett added: "A cell is not 100% charged at 2v/cell, the real value
is 2.25 to 2.27V/cell or 13.5-13.62V for a 12v (6 cell) battery"

So, here's what I found:

$4.99 HF charger stays on all the time and holds the battery at 13.25V,
installed in a modern vehicle (Audi S6).  

$29.99 Black & Decker float charger maintainer (I have) installed to a
charged battery charges briefly (less than a minute) at 13.6V then turns off
and lets the battery slowly drift down to 12.8V (which can take a day)

$49.99 Schumacher float charger (I have) installed to a charged battery
charges briefly (less than a minute) at 13.6V and lets the battery slowly
float down to 12.9V (which can take a day)

For reference, a fully charged battery with no surface charge measures
12.68V.

According to battery experts, the more expensive units should be better but
I detect no differences in how these units perform in the real world. I have
two of the $49.99 units, one of the $29.99 units and five or six of the
$4.99~$7.99 HF units.  All of them are in use all winter long and I've been
using all of them for many years.
Craig Nicol