On May 27, 12:20 pm, navti wrote:
after 18 hours if charging they are at 12,54 volts,

any thoughts ?

Is that;
1] 12,54 volts with charger still attached and charging?
2] 12,54 volts with the battery connected to nothing but a digital
Volt meter?
3] 12,54 volts with the battery now "running" 3-15 amps [whatever
your normal boat's usage is]?

If 1, you definitely have a bad cell [or your charger is broken].
Should be 13.6-14.4 [14.4 at the start {batt. dead} to 13.6 trickle
charging the fully charged batt.] unless you have a 'smart charger' or
reconditioner
If 2, This is totally meaningless data, all that most people ever know
of batteries, and how battery salesmen make their fortunes...[this is
"surface charge" you might have heard of...]. In a liquid battery,
this should stay at 13.6 for quite some time after removing the
charger [AGM's, with their inherently defective chemical nature
pointed out so eloquently by {I believe} Larry earlier, will usually
show something less depending {I reckon} on their quality], But even a
battery with a known dead cell can show this phantom voltage, so pay
it no heed!!!
If 3, looks promising. You still have to do the discharge test [run
10 amps for 11 hours, or 2 amps for 55 hours] to know if 110aH battery
is "good"