Wet cell vs AGM batteries

[REBrueckner]

The "Battery Terminal" discussion got me thinking about battery longevity. And mumbling a bit to myself....

It's interesting, and always distressing, to see how fast wet cell (lead/acid) batteries can reach the failure point of no recharge ability. This September, while returning from my six months cruising I noticed I was charging longer and (as usual) did not pay close enough attention. With a week or two my TV picture was contracting and that's when I checked the 2 house batteries with a hydrometer...not good...

When I checked my records I found I had replaced four of my six deep cycle 8D's with six months of each other just three and three and one half years ago...So I checked two others and they,too, were lower...so I replaced them while away. Unfortunately the best price I could get was $237apiece vs $197 at my home marina...

I only use distilled water, keep the batteries dry and clean, never discharge below about 30%, recharge them daily, use only smart charge alternaters and battery chargers, keep them on smart charge all winter in a heated boat, use a desulphator full time and have smart chargers. The only thing that is not so good is engine room heat, but even there I fan cool for an hour or two or hatch vent with the engine room door open after main engine running. It frosts me they don't last five or six years as in "the good old days". I've had the same (crummy) experience with Interstate and Powermaster. And maybe a pair of Exides several years ago.

I'm coming to the conclusion that AGM's are likely cost effective on a $/cycle discharge basis, although first cost is substantially higher. While the bulk charge limit for wet cells is only about 25% of amp hour capacity (meaning a 220 amp hour 8D will only accept a maximum of about .25 x 220 or 55amps), an AGM will accept 100% (or about 220amps) when sufficiently discharged. That can mean faster charging and less genny run time. Their higher RATED discharge cycle life means, in general, many more amp hours total can be provided over their life (IF the rating is accurate).

Anybody switch to AGM from wet cell for house use and what's your experience?

 

[Genesis]

I've run them exclusively on all my small boats for close to five years and the only reason they didn't go into Gigabite was that my batteries hadn't failed in there since I brought the boat home yet!

I like them. I don't like the price, but I do like their characteristics, deeper discharge capability, no acid spills or boiloff, very low self-discharge rate, etc.

The "gotcha" is that if you boil one its toast, and they're damn expensive.

I love the technology. Whether they're worth it if you rewire the house bank to run Golf Car batteries is another matter. Those can be bought cheap enough that it may not make sense economically.... but if you're going to stay with the 8D size then I suspect they likely are worth it on a per-cycle-of-use cost basis.

 

[Maynard Rupp]

We have been paying $150.00 for standard 8D batteries at our local marine store, "Mike's Marine". At that price and with about a three year life, I find it hard to justify any added battery expense. Now, the weight of these things and the sore back you get from changing them is another story. I am super glad that our '86 36C has them right below the engine room hatch. I can't imagine how you guys that have them outboard of the engines manage that task.

 

[Trojan]

I do the same as you do Maynard. I've done that for years on all my boats and farm equipment. I can't justify the difference in cost. But then I don't hang on the hook like you southern boys do ether. I don't run my batteries low. It's only my opinion but I think longevity is a product of slow recharging. Recharging heats the battery and heat kills. A low amp, slow charge keeps them cool. I never do a fast charge.


BILL

 

[yachtsmanbill]

Yesterday, I priced a 1400 amp 8D Interstate at my motor parts store where I usually get 40% off list. The 8D was 169.00 plus tax I just got back from SAMS other club, A place that I DETEST and paid a whopping $80.00 plus tax for the SAME Interstate 1400 amp battery that has a 6 month FREE replacement and 36 pro-rated warranty. At that point, they are disposable. IMLBB (in my little black book) One of the major rehab items on the 58 is to convert the ENTIRE system over to 12/24 volts. That being said, I will have 2 fresh starters,2 fresh alternators, and at least one bank (4) 8V19s and a host of pumps and a new CHARLES battery charger (all 32VDC ) to liquidate. The only concern is what do I do with my PERFECT IDEAL windlass? ws

 

[doc g]

I believe that that windlass motor comes in 24 volt,you can liquidate the 32v motor to offset some of the expense...............Pat

 

[yachtsmanbill]

THAT would be a blessing !! ws

 

[Pascal]

last time i did the math, $ / AH / Longeivity, cheap golf cart batteries coudn't be beat... $320 per bank/engine/4 years... or $120/220AH/2 years so far on the inverter bank.

" It's only my opinion but I think longevity is a product of slow recharging. Recharging heats the battery and heat kills. A low amp, slow charge keeps them cool. I never do a fast charge"

when back in the slip, I usually set the inverter/charger remote to a low setting, in part because i can't pull a full charge + all ACs in summertime but also to keep charging rate low... I only recharge full blast (140amps) when anchored in winter and i want to keep genset runtime to a minimum.

 

[jim rosenthal]

I have had pretty good luck with standard wet-cell batteries, but I don't anchor out very much.

One thing most of us fail to do is improve the regulators. The standard regulator that comes in an alternator on a marine engine is a dumb, one-stage regulator. Switching to a Balmar or similar multi-stage adjustable regulator makes a big difference. Usually the alternator charging capacity is fine, but the internal regulator doesn't make anything near full use of what the alternator can do.

If I start anchoring out etc, I plan to switch to AGMS. They do cost a lot, but they also last a lot longer, and if you have smart regulators and a good intelligent charger, they won't get boiled.

 

[spartonboat1]

Random comments:
I usually replace my 8D's with each bank off-cycle to each other...min 3 years, up to 4 years life. So when one bank is down/gone the other is at its half life of about 1.5-2 years and still has juice that can be called with the double pole switch.

Coast Guard in upper Great Lakes is reported to run AGM batts on their big rescue boats and after 7 years, no replacement needed...but anecdotal...

I was told by surveyor that I have the special charging regulators mentioned above. For some reason, until I get to above 1,100 rpm they don't really call the alternators...then quickly jump to a decent charge rate of about 14-14.5v (my old Mercedes manual stipulated 13.7-14.5 was the best charging rate for a nominal 12v batt, which showed 12.5v after charging). But they act like the inverter and don't continually overcharge, but "float". However, I run an inverter, so they call some juice all the time.

I seem to get a defacto "equalization" charge, when I run my genny which puts out over 15v for some reason (the setting obviously), but I have left it there. If one battery seems weak, the genny charging it seems to knock it back to life.

If you have a combo inverter/charger, such as by Heart (Xantrex now?), then you have an "equalization" cycle in the software that can be engaged. This cycle puts out about 15.5v at a declining rate on the batts for about 8 hours...really boils the fluid. But it stirs up the battery, and probably puts the material that has fallen off the plates to the bottom, where it shorts out the cell, back on the plates, and lengthens battery life. Needs to be performed a couple times a season. Its described in the Heart manual.

A different post mentioned the terminals and coating them. From what I understand from my 89yoa father, it is the positive terminal that needs the coating and will build up the oxidation. The negative is far less subject to that. Of course I still coat them both.

Replacing the 8D is a two person job...I tie a rope to each handle and the tech and I both pull, one to an end. When I can't lift the 75#'s with two arms, then time to get out of boating. (lift with your legs, not your back ).

my 2cw...

 

[spartonboat1]

Yesterday, I priced a 1400 amp 8D Interstate at my motor parts store where I usually get 40% off list. The 8D was 169.00 plus tax I just got back from SAMS other club, A place that I DETEST and paid a whopping $80.00 plus tax for the SAME Interstate 1400 amp battery that has a 6 month FREE replacement and 36 pro-rated warranty. At that point, they are disposable. IMLBB (in my little black book) One of the major rehab items on the 58 is to convert the ENTIRE system over to 12/24 volts. That being said, I will have 2 fresh starters,2 fresh alternators, and at least one bank (4) 8V19s and a host of pumps and a new CHARLES battery charger (all 32VDC ) to liquidate. The only concern is what do I do with my PERFECT IDEAL windlass? ws

==============
I just had to take a look at Sam's Club 8D's, which I finally did today. They now have the Energizer Bunny brand of 8D and the 1400 CCA was $131. While more than the $80 above, $131 is much lower than the $240 I have paid at a commercial source in the past. Since there are only about 3 producers of these wet cell 8D's in the US, they have to be a decent battery.

Just an update, but thanks for the Sam's mention above...