"Exercising" lead-acid batteries

In November 2011 I purchased two 90amp hour deep-cycle lead acid batteries to replace the my two elderly house batteries. Yesterday, 16 months later, One of the batteries is dead - bad cell confirmed with a load tester. I thought my batteries were living in battery-heaven as they are continuously maintained using an 85 Watt QPR solar panel and dual charge-controller. They have seldom been asked to do more than run my refrigerator for a few hours. I was told today that deep-cycle lead acid batteries will have a much longer life if they are "exercised" (discharged to say 50% capacity) every six months or so. Is this something I should be doing?


BTW: These are the batteries in question MARINE DEEP CYCLE DC27 90AH . This is the only vendor of marine batteries in St. Lucia and the waranty offered is minimal.

"my batteries were living in battery-heaven as they are continuously maintained using an 85 Watt QPR solar panel and dual charge-controller."


Depends on the settings of the charge controller, peak voltage and float voltage .

How much water did they use per month?

FF: This is the charge controller. The voltages are: regulation 14.4v, boost 14.6v, and float 13.7v. It is hard to know if the controller is really doing what it should, but it appears to be: the LED's come on steadily when regulating and switch over to flashing when in float mode. I have confirmed the float voltage at 13.6v with a digital voltmeter. I have also tested all batteries with an hydrometer and all cells except the dead one are in the green.

I check the electrolyte levels every couple of months. I have never measured the amount consumed, but I estimate around 50 to 100 cc's per cell. The dead cell required about double that when I checked the other day.

The question again: should lead acid batteries be partially discharged every few months, or just kept at the float voltage full time?

I'm going to go against all beliefs here so hang on.

I never ever leave a battery charger on constantly. I have a smart charger too, a Prosine.

Why? because batteries need a rest period after charging and a discharge before recharging. I started doing this in 86 with a boat I had then. It had a starting battery that was a Sears 48 month. I replaced it when it was 87 months old. Sears said they didn't remember selling that battery, a green pea I guess.

Since then, I've moved to my GB 42 and I have a starting bank and a house bank. My house is made up of 6 volt 240 amp batteries and right now they are 10 years old. I cycle them.

Go on Trojan batteries home page and I think there is information about cycling batteries. The life if a battery is only so many cycles. So lets say your battery had 1800 cycles, if you used them up with micro voltage charges that's why it died early.

I don't ever leave a battery charger on. I was a salesman and I know sales talk. Those chargers brochures are full of sales talk. Be wise, research and use the charger when needed. Your batteries will live longer.

I never ever leave a battery charger on constantly.

This is the new charge profile by Mastervolt that will soon be copied by the lower tier folks.

13.7 is a high float voltage , probably more suitable for start batts or a small fish boat with electric trolling motor.

I agree switch it off , if it is not required by the bilge system to keep the boat afloat.

Every other weekend would service OK house batts.

Thanks FF. I didn't know Mastervolt made chargers like that. I definitely will look into replacing my Prosine with one. That will help with my ageing brain and CRS.

Caphead,
I've always been of the same opinion as you and let my batts sit for 2 or 3 weeks and then charge them fully and repeat.

Bought new AGM batts recently and proceeded to do the same. Lots of other people said it's best to keep them in "float" status so I called Boat Electric in Seattle (where I got the batts) and they said to leave them on the "smart charger" all the time. The Zantrex charger cycles a bit up and down I think but Boat Electric said positively not to cycle them as I had been and to let the smart charger do it's thing continuously.

Charging continuously w a 2 amp charger may not be good - don't know.

And so I've done since. By the way Boat Electric is a long established 100% marine battery and service center. All who know them should be inclined to assume they have the last word on such issues. Call them if you like. They are on Westlake ave on the east side of Lake Union.

On one boat, I have a small 10A, 2 bank, smart charger and for 20 years I have left this connected all winter while the boat is stored, never had a problem. Float means float doesn't it?

On the other boat, I wire the banks together and connect them to a small 1 sq' solar panel and leave them all summer. Never any problems with it either all batteries have far outlived their warranty periods.
Agree with others that 13.7 may be a little high for float.
Just my 2c

Capthead said:

I never ever leave a battery charger on constantly. .

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I'm with you there.

I've had great luck in doing the same with all my batteries. cordless drills, portable equip, Fish Finder batteries, trolling motor batteries...etc.

I get a twinge when I see my friends cordless drill batteries sitting in the charger full time.

Brooksie,
I think 13.75V is float for AGM batts. My Zantrex was set up, installed and adjusted for my AGM batts and I asked him (marine electrician) about the 13.75V and he said that's what it should be.

Fishbucket,
Did you see my post #7? I'm a convert from your practice and still "feel" like I should take them off the charger but I don't. I used to turn off my shore power for about 3 weeks.
Where is Petaluma .. what state ? .. just had a flash ... Cal?

manyboats said:

Fishbucket,
Did you see my post #7?
Where is Petaluma .. what state ? .. just had a flash ... Cal?

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Yes... I saw it, I'm just not convinced yet.
I've just had great experiences to the contrary. " Smart " Chargers are a few steps ahead in tech now... so there may be hope for me.

And yes again. Petaluma is 40-45 mins. north of S.F.
I don't believe there is another one with that name in the whole USA.... maybe the World.

I used to have a dumb 50 amp Ferro-resonant charger, which I wouldn't leave on all the time. In those days I relied on my alternator to bring the batteries up, so I put in a 120 amp alternator and a smart regulator. That did the trick and I always got long life from my batteries. About 10 yrs ago I put in all new batteries, changed from 8D house to golf cart size, but kept the single 4D size for starting. Also upped the charging capacity by putting in a Xantrex MS2000 Inverter/Charger that puts in 100 amps and is itself "smart". Batteries now 10 yrs old and still perfectly fine. I leave the charger on at all times I am not away from the dock. I no longer depend on the alternator to to the heavy lifting. The smart aspect of the Xantrex extends to having an "Echo" for the start battery, which is obviously the right solution there too. When away for extended cruises, running the Genset for a couple of hours a day (needed to keep a supply of hot water) is enough to keep the batteries up.

"When away for extended cruises, running the Genset for a couple of hours a day (needed to keep a supply of hot water) is enough to keep the batteries up."

A solar panel might keep the batts up, and when the charge is over there are 12v or 24v elements to install in a water heater?

FF:

Solar panels? Here I side with Marin, who adamantly claims we never see the sun from where he is in the PWN to where I am in SW BC. We certainly don't get enough reliably sunny days to ever dream of using solar power for anything important.

Shoalwaters said:

I Yesterday, 16 months later, One of the batteries is dead - bad cell confirmed with a load tester. .

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The dead cell is likely unrelated to the charging system. The three major causes of dead cells are

• poor (think drops or banging) battery transportation from the factory
• running dry
• or faulty manufacturing.

Dekas are pretty good so I'd lean toward the first two as the dead cell cause. I leave my chargers on 24/7 (Newmar for engines and Magnum for house). In underground mines the LA lamp light batteries are successfully charging 24/7 on many decades old charging systems with in some cases many hundreds of batteries lined up getting their juice.

FWIW, I've been leaving my house bank (two Deka g31 AGM's) floating on the Freedom 10 inverter/charger w/ Link 2000 regulator/monitor set to "AGM" for 6+ months every winter. Last set lasted 11 summers of cruising.

Hi Richard,
The way the Boat Electric guy explained it to me was that what wears a battery out is discharging and recharging. So a constant "float" is best.

Yup.. . . I agree with that. (I killed a set of 8D's in 2 years using a defective charger) Replaced with a Xantrex Smart charger and the same type battery lasts for up to 11 years before I cycled them out due to their age. Either have your batteries on a Smart Charger or keep the charger turned off between visits to the boat. Over charging or keeping them too hot will definitely kill a battery in a year or two. The solar charger would be the unknown part for me??
Also you mentioned there was one dead cell. Did all the rest of the cells test OK with a hydrometer? If so, that sounds more like a defective battery than a case of overcharging.
JMHO
Larry B

Larry,

It was just one dead cell - all the others were within acceptable limits according to the hydrometer.

So, probably a faulty battery. I will continue using the solar panel/charge controller setup and see what happens.