I have a 2005 280 Sundance When...

[Frankie_T]

I have a 2005 280 Sundance

When I anchored my batteries run down even when using the generator, I sometimes run on batteries for several hours anchored,

 What is the best setting to have the batteries on when anchored for several hours?

[wingless]

Welcome to the forum.

My initial guess is that the batteries are defective, with the capacity failing to satisfy the nameplate rating.

A battery is considered to be End of Life, EOL, when the capacity fails to exceed the nameplate Ampere hour, Ah, rating.

The two ways to quantify the Ah for a battery. One is to either measure it w/ a meter, resembling a multimeter, except the AC conductance is measured and then cross referenced to an internal lookup table, specific to that particular battery.

The other way to quantify the Ah of a battery is the Old School method (my preference). Fully charge the battery for 24 hours w/ an appropriate charger. Remove the charger. Apply a load that would fully discharge a battery in 20 hours. That is, if the nameplate rating is 100Ah, then apply a 5A load. I like to use my carbon pile load for that testing. Measure the run time. The battery is okay if the run time exceeds 10 hours, greater than 50% capacity and must be replaced if the run time is less than 10 hours.

Fully recharge the battery for 24 hours.

Note there are other possible problems, like bad electrical connections that should all be checked My initial guess is the battery capacity is insufficient.

[wingless]

Prior typo fixed: A battery is considered to be End of Life, EOL, when the capacity fails to exceed 50% of the nameplate Ampere hour, Ah, rating.

[Frankie_T]

The batteries are all new

[wingless]

The fully charged batteries have an Ah rating. Is the starting point with fully charged batteries, properly charged for at least 24 hours?

Has the Ah capacity been measured on the new batteries?

A load is applied to the battery, such as a refrigerator sucking out 10A for 50% of the time, or a loud stereo sucking out 20A for 4 hours. How does the measured / calculated load compare to the expected run time? In this example, a 100% of nameplate capacity 100Ah battery will support just the 'fridge for 2 days.

My boat is setup from the factory with three battery banks, with different loads wired to each of the banks. Is the problem only on one bank, assuming the boat has more than one bank?

If the batteries are good, and the loads should be supported for longer than existing, then the problem is the wiring distribution. With a decent load applied, 5-10A, measure every positive and negative power distribution cable for excessive voltage drop. There should be less than 0.5V drop from the battery to the load, when providing a decent load current.

[wingless]

Correction: "In this example, a 100% of nameplate capacity 100Ah battery will support just the 'fridge for 2 days." That example would support the 'fridge for 20 hours.

[JerryF]

With generator running batteries should be getting a charge from the genny/battery charger. Make sure no breakers are tripped along the charging circuit. I bumped a breaker on my other boat while working in the bilge and only discovered it after thinking I got bad batteries. Throw a voltmeter on the battery with the genny running you should be getting at least 13 charging volts. If not trouble shoot the charging circuit. Check the obvious first...breakers.

[NickNweekender2]

As far as the volt meter goes I hooked up a quick charge dual charger with meter in place of the old 12v power plug in... I got mine on amazon for $15 and used a uni bit to widen the hole to 1 1/8"... now I have constant digital reading...