A few days ago while getting ready for the boating season I found that one of my three batteries was dead, 1.8V on the multi-meter dead. The battery, group 29, was purchased new roughly 6 months ago. All batteries are connected to a three bank, 10/10/10 charger that is approximately 16 months old. It’s a smart type charger that will apply the charge to each battery as needed. Interestingly, the battery status indicator on the charger shows that all batteries were fully charged when in the regular mode and fully charged in the individual “test” mode.

The dead battery is the starboard engine starting battery which also serves as the house battery (expect for the engine compartment bilge pump). The boat has been connected to shore power the entire winter so the batteries, theoretically, have just been maintained by the charger. All toggle switches have been off (except bilge pumps) but the battery switches were in the “ON” position. I assume that I have something drawing power. CAPAC shows a consistent “0.6”. This has remained unchanged since we purchased the boats (whether with old anodes, new anodes, over the side guppy anode).

I pulled the battery and charged it using a standard charger with a deep cycle mode. It now shows 11.38 volts, however the charger gauge shows 0% charged. I recall that I had a similar problem a few years ago which is what led to the purchase of the new 3 bank charger.

If anyone has any thoughts, I would love to hear them.

Roger: that shouldn't have made a difference if the charger was on all the time.
Walt: The battery may be defective. At 6 months of age, it should cost little if anythihng to replace it. CAPAC reading not relevant. Oh, another possibility is defective charger.

Distilled water only, tap water has limestone minerals that destroy your acid.

Lots of "new" batteries go bad because they are not new.
When you trade in an old battery the lead plates are either melted down and recycled or
they are reused in a "new" battery with new acid in a new case and sold to us as new.
If they are reused, there is a higher probability that they are defective.

If it's being drained by some parisitic load, it would have to be more amps than the charger is supplying to that bank.
You could test the draw on that circuit by substituting a known good battery and using an ammeter to see if there is a vampire somewhere in that circuit.

I would mark that particular wire from the charger and swap it with one of the other battery banks to see if the problem follows the wire.
Just be sure to check it frequently before another battery is ruined.

11.38 volts is less than zero. A discharged battery runs around 12 volts, and a fully charged one at least 12.6 volts. It really sounds as tho the battery is not being charged.

I have a solar battery mounted on the canopy above the cockpit. It is rated at 85 watts, I think, and delivers a couple of amps which I split between my two starting batteries. The start batteries have no other load on them, and the continuous amp of charge (during daylight) keeps them topped up when I am away. I have a smaller solar battery on the hood of my truck. I remove the negative terminal to kill the load, and let the sun keep my truck battery ready. My two house batteries are kept up by a float charger on shorepower that maintains about 13.5 volts. Of course, all four batteries are charged when the engines run.

I like the solar battery. No moving parts, no reliance on dock power, just keeps the start batteries ready. Once the engines start, there is juice enough for all.

I have found that the extra expense of Optima batteries is worth it. The AGM technology is excellent for boats.