Dead Batteries?

[johnmurray]

When my boat was launched yesterday (finally) the engine would not start because the batteries (a pair of 4Ds) were dead despite the fact that the AC current had been on in the boatyard and the battery charger in the boat was turned on. A quick investigation showed that the inverter was in the ON position and this apparently drained the batteries despite the fact that there was no AC load on the boat's electrical circuits.
I then switched off the inverter and plugged the boat into shore power at the dock and after about twenty minutes the batteries came up enough to start the engine.
There are three questions here: how did the inverter manage to turn on by itself (there is a remote touch switch in the cabin as well as a mechanical switch on the inverter itself); why would the inverter, even if it is ON, drain the batteries if there is no AC load; and since the batteries are original (came with the boat new in 2005) is is time to change them out despite the fact that there has been no trouble up until now?

[Pitou]

Not sure what gremlins turned on the inverter .. must be super natural. The inverter when in the "ON" position will put a small drain on the battery / batteries depending how the inverter is wired. I recall on my 28 it was somewhere around .3 amps / hour or 8 amps / day. At 30 days there's 240 amp hours and a weak enough battery to possibly not start your boat, again, depending upon how you are wired. A similar thing happened to me one winter. The gremlins came aboard and my house battery went dead. My inverter was isolated to just the house system and did not draw from my start battery. I caught it on a visit one cold winter day when the interior lights would not light up when the selector was on "House". I turned the selector switch to "Start" and my 12 volt panel came alive. The boat was plugged into shorepower so the AC panel got turned on along with the battery charger and all was good again in a short time.

Eight years with one set of batteries is a good long run for most batteries. Put a full charge on them and bring them somewhere that can put a load test on them. That's the only way to know of the their ability to hold a charge. I had a 4D one time that lasted 10 years before the load test got a little too low for my comfort and replacement followed.

Your issue could be one or the other or a combination. A load test will reveal a lot.

[Carl]

" since the batteries are original (came with the boat new in 2005) is is time to change them out despite the fact that there has been no trouble up until now?"

Depending on what the load tests on the batteries show, I would start by replacing either the house or the start battery this season. Then replace the other set next season so its not such a big hit all at once. If these batteries have been in use since 2005, they certainly do not owe you anything. As preventive maintenence I change mine out every 5 years, and have never had an issue on the water with the boat not starting. Water levels should be checked several times during the season if yours are lead acid. If they are gels, you might get more than 5 years of trouble free service, but I think 9 years is really pushing it. I am sure others will chime in.