Real life load test.....

[NYSail]

so new boat has a house bank of 2 4d lifeline agms 410 ah total. P/o said they were 5/6 years old. I have been very suspect of them. So I have been logging my monitor and watching my amps and ah along with voltage. Batteries fully charge at slip all week plugged in. Now on hook Batteries @ 12.4 v..... after 24 hours on hook 97 ah used. Put in new fuel filter (racor 500.... sweet) bled system and went to start...... engine turned over immediately. I let run while I checked fittings then turned off and went to turn back on and would not take load..... meter read "low". I had load tested them at the dock and they checked out..... they had been charged all week before I tested. So basically a false positive. Real life tells the story. So let me ask..... if you never cycle batteries meaning you leave them charging always and when you go out you turn generator on every day for a couple of hours to top them off.... never letting said batteries work a bit. Does it harm them and shorten life? P/o said that's what he did always.... my old boat I would work my batteries never bring them below 12.2 but damn near every weekend and they lasted and were very healthy it seemed 5 years (3 group 32 agm) till this day house bank will last 3 days with frig running cold and all accessories and still start engine with authority.

New batteries!

 

[dlochner]

Here's the answer to your question.
Darn AGM Batteries | SailboatOwners.com Forums

This is what Lifeline suggests for expected life, based on care.

• #1 Fully charge after each discharge. Estimated life: 6-9 Years

• #2 Fully Recharge at least once a week and equalize once a month. Estimated life: 4-6 Years..

• #3 Only recharge to 85% and equalize once a month. Estimated life: 2-4 years

• #4 Only charge to 85% and never equalize. Estimated life: 1 year.

AGM batteries have their advantages, tolerating some abuse does not appear to be one of them. I'll stick with flooded lead acid batteries. Also, 4 Golf Cart batteries yield the same capacity and are much easier on the back when installing and removing them.

 

[NYSail]

I fully agree.... ditching the 4d's.

 

[NYSail]

And yes read mainesails posts..... agm's have their place especially when located in confined areas.

 

[NYSail]

Don't think they were ever discharged

 

[SG]

You're saying that you used 97 amp hours (overnight); and the batteries were reading 12.4 VDC. You (more a man than me, changing a filter at anchorage for "fun") putz around, started the engine and then turned-it of. Then the batteries immediately show very low.

My guess -- you have a bad ground or discontinuity somewhere. You may have a connection -- but not enough of one to draw a load. If you have a "telephone" wire (e.g., small diameter), you'll show good voltage until you try to run your starter motor, windlass, or something material.

Was your refrigeration running? It's amazing to use only 97 amp hours over night.

Otherwise it doesn't make sense. I'd not blame your Lifelines. I have issues with Lifelines, but you're sound like they are doing fine.

 

[Stu Jackson]

It's amazing to use only 97 amp hours over night.

No, it's not:

Record of Daily Energy Use of 100 ah per day:

http://c34.org/bbs/index.php/topic,6353.msg41471.html#msg41471

 

[capta]

I agree that it sounds much more a wiring problem than a battery problem. Check all connections, especially your engine ground.

 

[NYSail]

After that point volts have dropped to 11.9. I switched to new starting battery that is doing fine. I am going after one suspect ground tomorrow...

 

[NYSail]

But wait...... so I continue to be puzzled and was testing batteries again with a direct meter to terminals rather than rely on boat instruments and was reading12.4 amps. As I had mentioned before I have some suspect neg wires right off the battery so figured what the heck. Rather than just sand and clean I decided to take a ride and have a new cable made..... 2.0 gauge and looks real pretty. Removed old, put on new and wow.... everything works. No dimming of lights when pumps come on engine started with an immediate drop of volts from 12.4 to 11.9 then right back up and as of the writing of this 15 hours later.... refrig and all accessories running, house battery still reading 12.3v. Also when was doing this I decided to bypass beneteau neg switch and go straight to engine. Figured I'd tie into the ground with all the other wires on the block.... the bolt looked real clean and good. However when I took the wires off, the block had a small rust spot right under wires so more resistance. Decided to put my new cable on a separate bolt on the engine until I can mount a proper buss.
So moral of this story is check and clean all your terminals, wires and connections for optimum service out of your batteries! Stu and Mainesail plus many more real smart guys keep saying this and it is so true. Don't assume it looks ok.
Again thanks to all who have chimed in on this and other battery posts I have written over pst month while I tried to figure this out! This forum really is invaluable and such a wonderful resource! Happy 4th of July.... let's go sailing!

 

[SG]

Good news. Don't badmouth you Lifelines (for a bit, anyway) :^)))

Was the cable you removed Marine Grade? (tinned, Ancor -- for example)

 

[NYSail]

Yes marine grade, however the install put the neg buss under the sea water impeller. I imagine salt water intrusion. Am going to cut open when I get home tomorrow , but it crackles when I flex it....