a shocking battery question

[Ron Churgin]

hey all,

The time has come to replace my house and starter batteries. I have a lot of questions.

First, I have 6 6volt 105 amp flooded batteries in my house bank. Will replacing them with 3 individual 12 volt batteries of close to the same amp hours give me the same capacity?

Second, I have been reading the posts about the pros and cons of AGM batteries and have gotten from this that correct charging is critical to their longevity. My boat is usually hooked up to shore power and I have a charger and an older Xantrex type monitor.

If I go the AGM route is it necessary to get a different style and do I need a specific type of charger?

I have learned that AGM's are harder to maintain on a mooring, but I am very rarely in that situation.

Any advice? I have read many of the old posts, there is so much good information my head is spinning.

[Jeff Barnes]

Ron,

Here are some thoughts I assume 315 AH is sufficient for your boat, in which case three 12V group 31s will serve the purpose. I have used 600 AH capacity AGMs (4 6V batteries) for seven years without replacement and could not be more satisfied with their performance and durability. With AGMs you need to consider a a few things. 1) They really should be charged with a three stage stage adjustable voltage regulkator (bulk, absorption, and float stages). This ensures proper charging when the engine is running. 2) Your alternator really should be at least 75 amps (foryour 315 AH bank). Smaller is OK but it just means excessive charging time, particularly during the bulk phase. 3) Make sure your alternator wiring is sufficient to handle the alternator's maximum output current. The AGMs will likely draw evrything your alternator is capable of putting during the iniytial charge sequence. AGMs draw far more current than flooded batteries when they have bee drawn below 80% percent of theoir capacity. Also, the absorption phase voltage needs to be adjusted specifcally for AGMs (14.4V). 5) Make sure your shore power charger can be set/adjusted for AGMs. Older style chargers were designed for flooded batteries only. I will be replacing my AGMs with another set (Lifelines) later this summer, as they have out lived their natural life expectancy. I particularly like them because they can be placed almost anywhere and don't out-gas when charging. Unfortunately, there is a price premium for the AGMs which some would argue isn't justified. Perosnally, I think they're worth every penny. I'm not sure why folks have said they are difficult to maintain on a mooring.

Hope this helps.

Regards,

Jeff Barnes

[Ron Churgin]

Hi Jeff,

Thank you for your very understandable reply. I have a feeling my alternator is not up to the job, and my shore power is only 20amp plugged in from an outlet outside the house. I really do not do much cruising, mostly six or seven hour day sails with a few one or two night overnights. It seems I would be better off replacing the flooded cells I have with the same.

[jepomer]

For a reference point, I have a 210 amp-hour 24 volt battery bank (four 6 volt GC2 batteries — total of $300 from Sam's Club)) that powers a Torqeedo 2.0 Cruise electric motor. The batteries are from 2008 and have been used on two different boats. They have always been charged using an intelligent charger.

Last year we had a slip and used shore power only to recharge the batteries. This year we are on a mooring and recharge the batteries using a 100 watt solar panel and charge booster (which brings the voltage up to the different charging voltages for bulk, absorption, float stages for 24 volt batteries in my case). This charge booster was originally developed to recharge golf carts.

We sail typically twice a week, motor only as necessary (like full speed when we are late for the Wednesday evening starts). We have also motor-sailed for hours in light winds.

The point is, you do want to have a good three stage intelligent charger. I used a 12 amp two outputs for shore power charging. If your needs are reasonable (no AC, and other high amperage devices), solar power will recharge your house bank in most cases.

Buying quality parts is cost effective in the end.

[Maine Sail]

hey all,

The time has come to replace my house and starter batteries. I have a lot of questions.

First, I have 6 6volt 105 amp flooded batteries in my house bank. Will replacing them with 3 individual 12 volt batteries of close to the same amp hours give me the same capacity?

105Ah 6V batteries would certainly be an oddity? Do you have a brand or model # for them? You may be confusing reserve minutes with Ah capacity? They are not one in the same. If they are typical GC2 6V golf cart batteries the AH capacity will be somewhere between 215Ah and 235Ah's depending upon the brand. With six of them you could have as much as 675Ah's?

Second, I have been reading the posts about the pros and cons of AGM batteries and have gotten from this that correct charging is critical to their longevity. My boat is usually hooked up to shore power and I have a charger and an older Xantrex type monitor.

AGM's have many benefits and some drawbacks too. They LOVE to be fully recharged to 100% after each use. This becomes problematic on mooring sailed or full time cruising boats, unless you add solar. I work mostly on mooring sailed & world cruising boats and deep cycle flooded batteries often outlast AGM's, for most owners. Is this because AGM's are bad, heck no, it's because owners are bad. Owners far to often fail to treat the AGM conversion as they should have, as a "system based" installation. Add solar, charge them correctly, and with enough amperage, and AGM's can last as long as good wets.

If I go the AGM route is it necessary to get a different style and do I need a specific type of charger?

If you are going to lay out some serious cake for AGM technology you'll want a true "smart" charger. Lots of chargers call themselves "smart" but if they do not have a battery temp sensor then they are simply not "smart". If going with Lifeline AGM's you'll want a charger with a custom user charge profile so when you need to equalize them you can do it properly. Do not accept a charger that has one "AGM" profile as all AGM's have differing charge voltages they want to see. Odyssey for example is very different from Deka or Lifeline. Right now I think the best value in a shore charger is the Sterling Pro Charge Ultra or the Pro Mariner ProNauticP (same chargers co developed between Sterling and ProMariner). AGM's have a tendency to cook non fan cooled chargers...

I have learned that AGM's are harder to maintain on a mooring, but I am very rarely in that situation.

Yes they can be very difficult to get more than a few years out of if on a mooring with no alternative means of topping them up after use. Dock sailed boats do far better with AGM's than do mooring sailed boats.

Any advice? I have read many of the old posts, there is so much good information my head is spinning.

If you go AGM you'll also want to consider an alternator upgrade with external regulator and alternator AND battery temp sensors. You may also want to consider a serpentine belt set up too. I replace LOTS of alts cooked by AGM batteries. I have two Hitachi/Yanmar alts on my bench right now and both were fried trying to charge AGM banks. Last week I was brought in to fix an issue on a Cummins installed in very expensive power boat. It had burned through four factory 120A alternators in two seasons. Cummins had no clue as to why and they kept replacing them under warranty. Well, now the warranty is out and the owner is pretty pissed.. The 600Ah bank of Odyssey batteries is why..... Alt is getting an external regulator and alternator temp sensor to keep it from cooking itself. It will probably last another 10 years+..

The true cost of AGM technology is not just in the batteries in $$$ to Ah's it is in all the ancillary items you need to properly get the life out of them you should.. I have one customer who spent over $5000.00 this winter converting to AGM but it was done right, huge alternator, serpentine pulley kit, Balmar MC-614 regulator, alt temp sensing, battery temp sending Balmar Duo Charge with temp sensor, 100A shore charger, solar and MPPT controller, new battery wiring, battery switch, battery monitor plus the bank of Odyssey batteries and custom battery mounts. Sweet system but replacing his old wets would have cost him about $400.00..... When his Odyssey batteries die it will only cost him about $2050.00 because he now has the set up to support them....

If you want a very good "price" on AGM's, Sam's Club is selling the Deka/East Penn line under the Duracell brand. These batteries however are NOT deep cycle and DO NOT perform equally to Odyssey, Northstar or Lifeline AGM's. You get what you pay for in AGM batteries..

The Group 31 AGM with 105Ah's is just $166.00. Compared to the Odyssey PC2150, which is 100Ah's and $425.00, it is a good value but it will NOT take the abuse nor last like the Odyssey will.. The Deka is simply not in the same category as the Odyssey but it still an AGM.