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Jiminri 03-10-2013 08:09 AM

Battery life short? What to check?
When I purchased my boat in 9/12, the starting battery was completely discharged. So this winter, my boat yard pulled all the batteries out to load test them, and reported that they were not holding a charge. They recommended replacement.

House: 2 house batteries: Group 31 Gel Batteries
Starting: 1 Optima Redtop Starting Battery

According the the PO's maintenance log, these batteries were originally installed in 9/09 and so are only 3 years old. Moreover, the log says these batteries were installed to replace identical batteries that had been installed in 8/02. So, the first set went for 7 years.

Is the 3-year life of the existing batteries unreasonably short? Could the yard be wrong? Does this indicate that something in the charging system might need to be addressed? (For the last few years the PO only really day sailed the boat and kept it plugged in at his dock.)

Also, the price for the new batteries being quoted by the yard seems low. For example, they want $254 for a new G31 battery which is lower than I see at Defender, WM, etc. I don't mind paying less :), but is there something I need to check to ensure the replacement is a quality battery?


JimsCAL 03-10-2013 08:19 AM

Re: Battery life short? What to check?
Allowing a battery to sit discharged will kill it. I suspect that's what happened. I figure a good quality deep cycle should be good for 5 years, maybe longer. A starting or combination start/deep cycle (like a Diehard Marine/RV) is good for 3 or 4. That assumes good maintenance.

tommays 03-10-2013 08:31 AM

Re: Battery life short? What to check?
How do the battery's stay charged at this point in time ?

For example my boat lives on a mooring and they were always undercharged until i installed a solar system

Maine Sail 03-10-2013 08:36 AM

Re: Battery life short? What to check?
#1 The max charging voltage for a GEL battery should be 14.1V

#2 The Optima should be charged at a higher voltage

#3 Either one bank is getting over charged or one is getting under charged

#4 If on a mooring how are the batteries getting back to 100% state of charge?

#5 What parasitic loads do you have on your system, even with the battery switch off?

#6 How deeply are you cycling/discharging the bank when you use it?

#7 How are they charged? Alternator? Wind? Solar? At a dock?

#8 How are you monitoring your state of charge?

#9 How are they wired?

#10 What are the charge sources as in brand, model amperage etc...

#11 What are the charging voltages at the battery terminals when charging?

#12 Does the system use a diode battery isolator?

chef2sail 03-10-2013 11:18 AM

Re: Battery life short? What to check?
After you get done answering MaineSail's good questions, you will want to look at the whole system as a whole. Electrical systems are a whole entity on a boat as important as an engine and can't be piece mealed . Also it is an expensive system you can waste and save money in with good planning They are only as good as their weakest point.

So you have batteries, charging methods, amp hour load, monitoring to simplify it.

Ah load- what is your normal daily use. Calculate using refrig, pumps, electronics, lights, windlass, etc. This will allow you to determine whether you have enough or what you need in battery amp hour (ah) power. And how do you se your boat.? Weekends , wee is, days,

Charging methods. Do you have a modern 3 stage charger? Are you at a slip long enough to maintain 100 % charge, Do you have solar to maintain 100% charge while underway? What type of alternator? Do you desulfate you batteries if wet.

Batteries- you have two types t o charge gel and AGM, usually a no no. What batteries best suit your use, wet, AGM, gel. Are group 31 the best ones for you. In most instances I like 6 volts as their plates are heavier and you get as much as 3 but always twice as many deep cycles and usage out of a battery. Also if you can fit their height, 2 -6 volt will give you twice the ah as one group 31 in almost he same footprint. You could literally double you ah in you space by going to them and also double your number of deep cycles thus doubling you lifetime.

In this part read up on battery charging, 50% discharge. Charging back to 80-85%, time it takes to get back to 100%. Amount of usable ah. In a group 31 bank for instance each battery may be 110 ah. You can only discharge or have useable 50%. So you may have 220/2= 110 ah usable. If your daily ah diet is let's say 70-80 ( you have refrigeration) that's 1.5 days. If you don't have solar or the dock to recharge your engine may bring back o 85% or 187 ah the next day you se 70 ah you are own at he adage again 187-70=117 and this continues till you get back to the slip and can get back to 100%. In the 6 volt scenario you have 4 of them of 440 ah at 12 volts ( wet ones can be had for less than $100 a piece). So with 440 ah you have 220 available. You say out overnight and you use 70 so your down to 150 available ( 2 more nights without charging) and are at 370 ah which is almost the 85% you can get o without the solar or battery charger. You motor for a few hours. Battery acceptance is much lower past 85% so maybe you can only put in 20 ah so your back to 390. You stay out another night without the dock and use 70 more. Now yor down to 320 ah but 100 usable still in reserve. You motor two hours. With an average 50 amp alternator you re back to 370 ( 85%) in one hour. Then lower acceptance again. And so on. Maine sail will correct my figures, but you get the scenario. If you do weekends as most t least do having 440 ah capacity is never having to worry.

Also you must take care of the batteries. Desulfating if necessary. Temp control etc. most batteries should last 5-7 years easily if maintained. Otherwise gets expensive. AGM / gel are specialized batteries and have their place, but only if he whole system is up to snuff to keep them charged as they are only out effective if kept near 100%.

Monitor. That's how you keep track of the above. It's simple and cheap with the orrect monitor and you need to look at it a few times in a day quickly for 20 seconds o make ure its ok.

Do some reading and listen to Maine you will avoid lost of extra expense and aggrevation You won't worry bout power or adding something new to your boat.

gershel 03-10-2013 03:50 PM

Re: Battery life short? What to check?
I have 4-6v deep cycle gels that I use for house and starting. They are 13+ years old, and still appear strong. Sitting in the boat all winter, without being plugged in,they lose about 0.05v. I think charging at the proper volage has a lot to do with their longevity. I don't know how much longer the'll last. but so far Isee no end.

hellosailor 03-10-2013 06:03 PM

Re: Battery life short? What to check?
Jim, there could be a lot of stuff wrong but if the yard didn't say anything about the mixed battery types being a serious problem? They're greasemonkeys, use 'em for brute force labor but try to ignore anything technical they may say.

Mainly what Maine said. And if you look at other message threads, buy one of the popular and inexpensive "twelve volt" books for boats, or check around the web, you'll get plenty of answers. If a system is not set up from the basics, you can throw a lot of money at batteries, year after year. After year.

Take the time to learn the groundrules, and you'll be well paid for your time with the savings.

eherlihy 03-10-2013 06:16 PM

Re: Battery life short? What to check?
All of the batteries in the same charging source should be of the same type. The reason is that AGMs and GEL and wet-cell batteries have different charging acceptance at different voltages. Mixing GEL and AGM (which is what you have done) will lead to shorter life of one or both.

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