The recommended float voltage differs a fair amount with temperature and
with battery type (liquid, starved, or, now very rare, gelled
electrolyte). I'd check the manufacturer's specifications for the
specific cell. Most are on the web these days. If I were floating a
battery outside or in any other environment with substantial temperature
variation, I'd want to use a temperature compensated charger, with the
charger close to the battery.

Roy Lewallen, W7EL

Bob Lewis (AA4PB) wrote:
According to the manual the Harbor Freight charger is 15.5V. That
seems a little high for a float charge to me. 12-volt LA batteries are
generally float charged at 13.8V. Did you guys measure the voltage
with it connected to the battery or under "no load"?