Dead Batteries -- Blast Them or Coddle Them?

[Dockhead]

Originally Posted by senormechanico

A 100% charge will be 12.6 volts after battery has had 24 hours of rest with no load.

That's also my understanding.

But who while cruising can take all loads off for 24 hours? What do you think about my slightly loaded test? What do people really do in practice?

[Hud3]

DH,

I think the real (read "practical") test will be when you have them fully charged, go for a cruise and then see how long they last. If they discharge noticeably faster under normal use patterns, you've got a problem. Good luck!

[rtbates]

A fully charged 12v battery is at least 13.8 (wet) to 14.2(AGM)

you'll never get there IF your system thinks 12.6 is fully charged.

My heart felt condolences. I know I was really bummed when one of my $230 agm batteries went tits up..

I can't imagine $2k worth...

Something is very very wrong in your electrical system.

good luck

[btrayfors]

Dockhead,

Your logic re: voltages under light load is correct. It's the system I've used on my boat for over 20 years, and while I understand the logic and advantages of battery monitors -- like the Victron -- and while I have installed them in client's boats, I don't need one on my boat.

I agree that a compass light alone isn't the problem...you've got a leak somewhere. Until you find it, and assuming the bilge pump is connected directly to the batteries, then you might just take a cable off the house battery bank when you have to leave the boat, leaving the bilge pump connected, of course.

I assume you have Trojan wet cells (flooded batteries), and not AGMs or gels.

You don't have enough charging power on your boat to worry about "fast charging". Those Trojans will take all the current you can throw at them. And, of course, they'll dial back their acceptance level as they come up in charge level (State of Charge or SOC); then, they'll take what they're going to take, period, no matter the size of the charging source.

In numerous battery tests I've done over a two-year period we depleted flooded and gelled and agm batteries to 10.5V, which is generally accepted to be 100% discharged. They come back just fine, but you do do a bit of damage each time you discharge them that far.

If your batteries are new, it's unlikely that they're shot. They should come back just fine.

However, you might have a battery with a bad cell or two. It would be good to check individual battery voltages a few hours after removing the charging current. If they vary considerably one-from-the-other, then there's a problem. Also, if they're flooded batteries it would be good to check the specific gravity of each cell using a decent hydrometer.

Re: charging sources, IMHO solar panels are much to be preferred over wind generators, even in Merry Old England where the sun don't shine much :-) They're virtually trouble-free and last more than 20 years and have no moving parts and, coupled with a good MPPT controller and hooked up in series, will give good performance even in low light conditions.

FWIW,

Bill

[Dockhead]

Originally Posted by rtbates

A fully charged 12v battery is at least 13.8 (wet) to 14.2(AGM)

you'll never get there IF your system thinks 12.6 is fully charged.

My heart felt condolences. I know I was really bummed when one of my $230 agm batteries went tits up..

I can't imagine $2k worth...

Something is very very wrong in your electrical system.

good luck

Umm, I think you're confusing charging voltages with open circuit voltages -- two very different things.

Trojan recommends charging at 14.8 volts (28.6), with periodic equalization at 15.5 volts (31 volts). That's exactly how my Victron charger is set up.

Trojan say that open circuit voltage of 12.73 volts (or 25.46) is a 100% charge. Open cell batteries can't get to an open circuit voltage of 13.8 volts, and according to Trojan, overcharging is very harmful.


Well, I have good news -- my batteries seem to be ok or at least not badly damaged. Halleluijah! Although I did not manage to fully charge them over 3 1/2 hours this morning (they were still accepting 20 amps and had not reached absorption voltage), nevertheless they held over 25 volts all day long -- for seven hours with light loads on. As an experiment, I put on a 3kW inverter load on them, which pulled them down to 24 volts as usual. When the load was taken off, they bounced right back to 25 volts. I'll charge them for a few hours again this evening.

Now I need to get into a marina so that I can give them a good overnight charge on shore power, then equalize them.

I didn't really hope that these Trojans would be significantly better than the Varta leisure batteries that they replaced. But one such episode destroyed my Vartas last year. The Trojans do seem to be standing up a lot better! I didn't really expect it!

[Dockhead]

Originally Posted by btrayfors

Dockhead,

Your logic re: voltages under light load is correct. It's the system I've used on my boat for over 20 years, and while I understand the logic and advantages of battery monitors -- like the Victron -- and while I have installed them in client's boats, I don't need one on my boat.

I agree that a compass light alone isn't the problem...you've got a leak somewhere. Until you find it, and assuming the bilge pump is connected directly to the batteries, then you might just take a cable off the house battery bank when you have to leave the boat, leaving the bilge pump connected, of course.

I assume you have Trojan wet cells (flooded batteries), and not AGMs or gels.

You don't have enough charging power on your boat to worry about "fast charging". Those Trojans will take all the current you can throw at them. And, of course, they'll dial back their acceptance level as they come up in charge level (State of Charge or SOC); then, they'll take what they're going to take, period, no matter the size of the charging source.

In numerous battery tests I've done over a two-year period we depleted flooded and gelled and agm batteries to 10.5V, which is generally accepted to be 100% discharged. They come back just fine, but you do do a bit of damage each time you discharge them that far.

If your batteries are new, it's unlikely that they're shot. They should come back just fine.

However, you might have a battery with a bad cell or two. It would be good to check individual battery voltages a few hours after removing the charging current. If they vary considerably one-from-the-other, then there's a problem. Also, if they're flooded batteries it would be good to check the specific gravity of each cell using a decent hydrometer.

Re: charging sources, IMHO solar panels are much to be preferred over wind generators, even in Merry Old England where the sun don't shine much :-) They're virtually trouble-free and last more than 20 years and have no moving parts and, coupled with a good MPPT controller and hooked up in series, will give good performance even in low light conditions.

FWIW,

Bill

Thanks for that, Bill!

Thanks for confirmation about the method of measuring state of charge. Gives me more confidence. I will continue to do it that way. It seems to me that if this method gives different results from a true open circuit test, then surely it will err on the side of showing a lower state of charge than is really the case. That just adds an element of conservatism, doesn't it? Seems ok to me.

I have remote battery isolators. I did not isolate the batteries this time because my large bilge pump is not wired directly to the batteries. It was very rainy and I was worried about rain down the mast. I will not repeat that mistake. But in any case, I am going to take my DC clamp meter and track down the leakage.

I will also go through all the batteries (8 of them -- a time-consuming process) with my hydrometer to verify no bad cells. If I find one, it's not the end of the world to replace one or two batteries. I figure the elecrolyte is now highly stratified (the only way I could see such high voltages all day with only a partial charge) so it will take a a good equalization charge to stir up the electrolyte enough for the specific gravity test to be meaningful.

I wish I had gone solar as you suggested, and as Pete suggested last year when I was deciding on the wind generator. The wind generator was a big mistake. The bloody thing is rather useless, and I have a couple of grand invested in it -- I had it professionally installed in Cowes at great expense.

[hellosailor]

Dockhead, this is one reason we keep the compass light on the nav lights circuit and that gets shut when the Big Red Switch gets shut before leaving the boat.

But I'd agree with the others, especially when you say the isolated SLi battery was also pulled down, that there's something else wrong. Maybe a bad diode in a common point, like the alternator? That's a common reason for starting batteries to die, and easy enough to test.

While you're crawling around with the hydrometer...electronic (not carbon pile) battery load testers are now around $50 (up to 1200 CCA rating, a bit more for higher) on Amazon, you might look into one of those. You clip it to one battery, punch in the nominal capacity, it does a fast internal resistance test to tell you if the battery still has rated starting power. That's one good fast way to test "real" battery power.

As to saving your batteries...wet lead takes some permanent damage with each full discharge cycle. Some as any sulphites become insoluble after 30 days--which you're inside of. An SLI battery can be ruined by as little as 4-6 full discharges but deep cycles are way more robust than that, so by all means, charge 'em back up, keep a good charge on them for a while, see how they recover. Odds are you will have lost a little something, but they should still come back.

Then you might want to rethink what's on the Big Red Switch, and look for stray drains on anything that isn't.

FWIW, there are some "boat monitoring systems" on the market now that will do tricks like send you a text message if the batteries get too low. Compared to the cost of a new battery bank...might not be unreasonable. Although of course, that's one MORE system that can go wrong.<G>

[Dockhead]

Originally Posted by hellosailor

While you're crawling around with the hydrometer...electronic (not carbon pile) battery load testers are now around $50 (up to 1200 CCA rating, a bit more for higher) on Amazon, you might look into one of those. You clip it to one battery, punch in the nominal capacity, it does a fast internal resistance test to tell you if the battery still has rated starting power. That's one good fast way to test "real" battery power.

I actually have one of these -- a good one which cost about $300. I am not entirely convinced of its accuracy. But I did test and log results for every one of the 8 new batts when I installed them in February. I will test them again. Might show up any bad batteries. But my impression as of this moment, anyway, is that they are as strong as they ever were. We shall see.

[btrayfors]

I've found the $600 range testers by Midtronics to be very reliable in measuring capacity with flooded batteries (compared to results obtained with a true 20-hour load test). They are the industry standard.

They also work with AGMs, but not as well, tending to overestimate capacity due to the very low internal resistance of AGMs.

Remember, the voltages you're seeing only represent the state-of-charge (SOC) and, while related somewhat, SOC and battery capacity are two different things. You'll only know for sure about the capacity of those batteries when you go cruising!

But, my bet is that this one slipup in discharging them nearly 100% probably did very little damage, assuming they weren't left in that state very long.

Good luck,

Bill

[Dockhead]

Originally Posted by btrayfors

But, my bet is that this one slipup in discharging them nearly 100% probably did very little damage, assuming they weren't left in that state very long.

Good luck,

Bill

Thanks.

I was away from the boat for 20 days. I don't know when they reached the 8 volts at which I found them I would say it was a total, 100% discharge

This identical situation permanently ruined an almost new set of Vartas last year.

But so far it seems the Trojans are ok after such abuse. A credit to Trojan batteries, I guess, if it really turns out to be so. I'll know more over the weekend after I get a shorepower overnight charge on them, and to specific gravity and capacity tests.

[Stu Jackson]

Sorry to hear about your loss.

Try reading the Ample Power Primer, here: Technical Documents, Manuals, App Notes

If you did the same thing twice, you might want to consider rethinking your DC wiring arrangement so when you leave the boat, everything is turned off (except for wiring your bilge pump to your house bank, and maybe your stereo memory power) instead of doing this again.

[sailinglegend]

Originally Posted by Dockhead

....But who while cruising can take all loads off for 24 hours?.....

Just disconnect one battery and leave that a few hours to test the open circuit voltage. Next time disconnect a different battery.

[hellosailor]

"Just disconnect one battery and leave that a few hours to test the open circuit voltage."
The advice I've seen from multiple battery makers is that flooded lead batteries require a full 24 hours for the electrolyte to equalize out and the surface charge to dissipate. Not a few hours--but overnight to 24 hours.

As an alternative they also "all" make the same suggestion, put a load on the batteries for 3-5 minutes and that will pull off any surface charge. (Won't help the electrolyte equalize but will pull off the surface charge.) With a car they suggest putting the headlights on for a while. With a boat, you'd be looking for a similar load multiplied out times the # of batteries.
A few hours might very well work--but not to the same accuracy. Retest your batteries after a full 24 hours, and you should see the difference.

This is also one of the invisible differences in battery brands. Some years ago Sears(?) made a big deal about SLI batteries that had a unique design which was supposed to make the acid circulate and equalize out much faster than the usual. I suspect this adds either cost or volume to the battery.

[Fuss]

Originally Posted by Dockhead

I have another question -- how do you guys monitor our battery charge state? I have a Victron battery monitor which counts amps in and out. Because of the way it is wired, I don't trust the amps-counting function and don't pay that much attention to it.

The Victron battery monitor tells you how many amps are going out or how many are coming in.
You say you dont trust it. I would suggest getting it wired properly. It is a very important instrument that would have shown your compass light drain and any other drain.

When I leave my boat it is the last instrument I look at.... I expect to see 0.00 amps. I then know there is no drain. I then switch on the solar and expect to see +2 amps roughly. Then I leave.

If you had it wired properly and trusted it, you would have seen the drain earlier.

The victron monitor is easy to wire up and goes on the negative near the battery. If there are other negative cables to the battery post which effectively then bypass the monitor then its wired wrong.

Of course if you wish you can leave it wired incorrectly and use the clamp meter.

But one thing is for sure, you have to do this amp test with either a correctly reading monitor or clamp meter as the last thing before leaving the boat every time.

[Dockhead]

Originally Posted by Fuss

The Victron battery monitor tells you how many amps are going out or how many are coming in.
You say you dont trust it. I would suggest getting it wired properly. It is a very important instrument that would have shown your compass light drain and any other drain.

When I leave my boat it is the last instrument I look at.... I expect to see 0.00 amps. I then know there is no drain. I then switch on the solar and expect to see +2 amps roughly. Then I leave.

If you had it wired properly and trusted it, you would have seen the drain earlier.

The victron monitor is easy to wire up and goes on the negative near the battery. If there are other negative cables to the battery post which effectively then bypass the monitor then its wired wrong.

Of course if you wish you can leave it wired incorrectly and use the clamp meter.

But one thing is for sure, you have to do this amp test with either a correctly reading monitor or clamp meter as the last thing before leaving the boat every time.

My boat used to have two different "service"banks, with the windlass, winches, and thruster on their own separate bank. I combined these banks, which turned out to be a very good decision. But the two banks have their own negative bus bars. I just had everything rewired by an expensive professional marine electrician to go to one master negative bus bar, so in theory, the Victron meter should be getting all of the loads. But in practice there are some exceptions -- the engine-driven alternator, for example, doesn't get its negative through the bus bar, and the Victron doesn't count amps added by the alternator. I'm not totally sure yet whether there are other exceptions; hence I do not entirely trust it -- yet -- for counting amps.

The first time I killed my batts, it was because of a cycling bilge pump. This time, it was because of my own stupidity -- I did not isolate the batteries. I have a master remote isolator switch that disconnects -- theoretically -- all the loads except one bilge pump. The reason for that was I assumed that my shiny new wind gen would cover any tiny loads, and I wanted my second bigger bilge pump switched on because of the monsoon-type rains we were having. Shame on me.

But your point is well taken, and your procedure is helpful -- I will do it. I have a good clamp meter. I will carefully check the current next time I leave the boat. I isolated the batteries yesterday, by the way, for the day when I went up to London for a meeting. The drain shown on the Victron was not 0.00. There was small current -- 0.1 or 0.2 amps, I think. Could have been the backlight in the Victron meter, and/or the water sensor in the bilge pump, I guess, but such a current should not kill batteries, even with my useless wind generator producing zero power. 0.2 amps over 20 days is 96 amp/hours, which should be within the abilities of a fully charged 420 amp/hour battery bank to handle, I would think.