Batteries? Charger?

[drynoc]

I have two three year old West Marine batteries that refuse to turn over the starter on my nearly new Yanmar, even though the Vector smart charger that I have claims that they are fully charged. In fact, they won't even run the little bilge pump that I installed. Is it possible for fully charged batteries to not work properly? Or could it be that there is something wrong with the charger and it doesn't know bad batteries when it sees them? Both batteries have plenty of water, and I re-conditioned them both using the charger for 48 hours last weekend.

[CapnHand]

Most chargers indicates a full charge when the batteries will no longer accept any current. That doesn't mean that the batteries will hold a charge. Chargers do not test batteries.

Battery testing info here: http://www.batterystuff.com/tutorial_battery.html
Or if you take them to a garage, they can test them for you.

Chances are 95% that the batteries are toast. Batteries will only take a finite number of charge / discharge cycles. Three years is about the limit for "Marine" batteries. Lots of people replace their batteries every two years before they get to the stage yours are at. If you get true deep cell batteries, you may get two or three times as much life out of them, but they cost more.

[US25]

Is it possible your connections have oxidation? I'm guessing there's no visible corrosion? but sometimes a thin layer of oxidation can be nearly invisible. Try cleaning the connections first and see if that makes a difference; you'll probably need to scrape off the oxidation with a knife or tool, as a wire brush normally won't cut it. Also, I borrowed a portable load tester from my auto mechanic once, it's the only real way to tell.

[drynoc]

Thanks for the replies. There is no oxidation or corrosion on the connections - I keep them scrupulously clean. The starter groaned once before quitting, and the bilge pump ran for about 30 seconds. So they are getting juice - they're just not getting enough. I had someone put a load tester on the batteries last weekend, and he said they were both OK, and that they probably just needed to be re-conditioned. I did 48 hours of re-conditioning on both of them, and then charged them. They both took a charge at the time, and both are claiming to be fully charged now, at least according to the charger.

[hellosailor]

Some of these new cheap chargers actually are pretty smart about reading battery voltage, but a hydrometer (I hate the acid mess) or voltmeter is a good cheap reality check.

You need to check the batteries with a simple load, like a car headlamp or clip-on spotlight, connected right to the battery terminals. If that stays bright, you know the batteries are OK, period. (A load tester isn't very expensive, but a spotlight can be used for other purposes.< g > )

If the batteries are OK and you still can't run things...you've got bad wiring someplace. Corrosion on the outside of the cable lugs? Or black rot inside the battery cables--if they are not made from tinned wire, they are rotting from the inside. Or further down the line, at a fuse link, at the A/B switch...somewhere there is a bad connection blocking the power.

[drynoc]

Thanks, hellosailor. I'll have the batteries load tested again just to make sure. I hate to think about it being a wiring problem, because I completely re-wired the boat two years ago when I replaced the engine. I used tinned wire for the entire project. I did not replace the A/B switch, however, and since the system is treating both batteries the same, that would seem to be a logical place to start. How would I test the switch to see if it is functioning correctly?

[hellosailor]

drynoc-
You could test the switch by checking voltage into it, versus out of it. Or disconnect the power leads and test it with an ohmeter, which should show near zero on all paths. Or, hook up that big spotlight to load test it across the switch.
This has the feeling I know all too well: "It's something simple, stupid." (Don't ask me why I know that so well.)

[sailingdog]

How deeply do you discharge the batteries between recharging them?

The deeper the discharge, the more quickly you will generally kill the batteries. Given that you're reading full voltage, but not getting any amperage out of the batteries, I would guess that they're dead.

[hellosailor]

"Given that you're reading full voltage, but not getting any amperage out of the batteries, I would guess that they're dead."
That logic would only apply IF he was reading full voltage under load. But even then, if the batteries were shot, that voltage under load would also plummet. A regular 12v battery in the best of condition may still show a mere 10V "under load" when the starter is engaged. The usual battery test for warranty repairs is to use a battery load test (aka carbon pile, maybe $30 to buy one) and to watch the battery voltage under a known load for a known time.

If you've got voltage under load--but no amperage--then there's actually no load, i.e. something is not allowing the power to flow.

[sailingdog]

Another question: The little bilge pump, how is it wired to the batteries???