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Old 11-10-2014, 15:48   #1
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Confused; Batteries/Chargers/etc.

I think I need to re-do the batteries and charger in my boat, but I'm having a hard time deciding which way to go.

Currently the boat has 3 g31 and 1 g27 gel batteries of unknown age. Guy I bought the boat from says he thinks the batteries were replaced in '06 (he bought the boat in 08), but the "date sold" on the batteries are all different. Year marks are "3", "9" and 2 "7"s. Since I know the guy I bought the boat from didn't replace the batteries, then I'm guessing the "9" must be 99, and I suspect the 7s to be "97".

I don't know the age of the charger either, but it makes a lot of noise when it's flipped on and during the survey it was noted that it was getting rather warm and only feeding about 12.7v to the batteries. I tend to leave the charger off unless I'm actually on the boat in case it decides to get really hot.

So now to my questions and confusion. I've only seen over 13 volts once on the batteries, most of the time the battery monitory says about 12.65-12.75v. Now, according to the "electrical study hall" thread, 12.75v equates to 100% charge, but in all the charger threads I've read everyone talks about reading 14.Xv on the batteries when they're fully charged. So which is it?

I know Gel batteries take a little care to set the boat up for, and I believe my boat was done properly. All Gel batteries, with a 3 stage alternator regulator, and (I'm guessing) a charger set for gel batteries. I don't want to deal with the maintenance of standard lead acid batteries so I'd like to stick with Gel or AGM. What advantage do the Gel batteries have over AGM? If I go with the same brand that is currently on the boat, The G31 AGMs have 8Ah more than the Gels and are $100 cheaper. Is it worth sticking with the Gels?

I'm also a little confused about what size charger I need. Supposedly Gels and AGMs can be charged with higher amps than normal lead acids, but even for lead acids, with the ~300Ah bank and charging at 25% of total capacity, I could have a charger rated at 75 amps. Nearly all the chargers I see though are only rated to 20-30 amps, with the occasional one rated at 50 amps. The 30 amp chargers seem like the appropriate size for my boat based on the manufacturer specs, but that would only be ~10% of total bank capacity then.
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Old 11-10-2014, 15:58   #2
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re: Confused; Batteries/Chargers/etc.

Hi & welcome.

If you've invested the time to read that, Good for You!

You might "enjoy" this, too:

Electrical Systems 101 Electrical Systems 101


Scroll through and find what hits the answers for you. To charge a 12.8V nominal battery, you need a higher voltage, like 14+V. Simple chemistry.

Chargers? Get rid of yours, it's killing your batteries, new or used. Don't get new batteries with that old charger.

Sizing depends on how fast you want to or need to charge. There'
s a charger link in that 101, too.

Happy reading, we've all BTDT.
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Old 12-10-2014, 06:29   #3
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re: Confused; Batteries/Chargers/etc.

Quote:
Originally Posted by blinkerfluid View Post
I think I need to re-do the batteries and charger in my boat, but I'm having a hard time deciding which way to go.

Currently the boat has 3 g31 and 1 g27 gel batteries of unknown age.

You might hum a few bars about which of your batteries do what. Is that 3x G31s as a house bank? 1x G27 as a starting battery? Or...?

-Chris
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Old 12-10-2014, 07:40   #4
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re: Confused; Batteries/Chargers/etc.

Quote:
Originally Posted by blinkerfluid View Post

So now to my questions and confusion. I've only seen over 13 volts once on the batteries, most of the time the battery monitory says about 12.65-12.75v. Now, according to the "electrical study hall" thread, 12.75v equates to 100% charge, but in all the charger threads I've read everyone talks about reading 14.Xv on the batteries when they're fully charged. So which is it?
To correctly charge gel batteries the charger should increase the voltage to about 14.2v ( this may take some time if they are flat). Then hold the batteries at 14.2v for around 1-2 hours. The voltage is then reduced to around 13.6v and kept there. (The exact ideal voltage depends on the make of battery and should be adjusted for temperature (lower in hot conditions).

You need to monitor the voltage over some time to see if your charger is doing this, but it sounds like your charging voltage is too low.

12.75=100% charge is quite different. This means when the battery is rested with no charger and no load (the rest period needs to be 24hours or so) a voltage of 12.75 is APPROXIMATELY 100% charged. This does not imply 12.75 is the correct charge voltage.

There are a lot of views on the ideal battery chemistry. My view is that good gel batteries give the longest life and cheap flooded batteries give the lowest cost on $ per year.
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Old 12-10-2014, 15:50   #5
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Re: Confused; Batteries/Chargers/etc.

Yes, 3 g31s for the house bank, 1 g27 for the starter.

The boat has a link 10 battery monitor on it. After running the engine for a little bit, the batteries will read just over 13 volts. However I've never seen over 12.7 with the charger on shore power even after the charger has been on for several ours. Sounds like my charger is toast.

It seems like the batteries are holding a charge from the alternator and the ac charger isn't doing anything at the moment. I'll start with changing the charger out, but I'm still not sure how long the batteries are going to last. I'll have to actually apply some laid to them and see how they discharge.
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Old 12-10-2014, 17:27   #6
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Re: Confused; Batteries/Chargers/etc.

Quote:
Originally Posted by blinkerfluid View Post
I think I need to re-do the batteries and charger in my boat, but I'm having a hard time deciding which way to go.

<snip>

I don't know the age of the charger either, but it makes a lot of noise when it's flipped on and during the survey it was noted that it was getting rather warm and only feeding about 12.7v to the batteries. I tend to leave the charger off unless I'm actually on the boat in case it decides to get really hot.

So now to my questions and confusion. I've only seen over 13 volts once on the batteries, most of the time the battery monitory says about 12.65-12.75v. Now, according to the "electrical study hall" thread, 12.75v equates to 100% charge, but in all the charger threads I've read everyone talks about reading 14.Xv on the batteries when they're fully charged. So which is it?
You haven't clearly defined the problem you are trying to solve - old age is not a reason to replace batteries or charger.

Your concern should be either, "batteries don't last very long when off charge" or "batteries don't get fully charged"

Batteries Don't Get Fully Charged - Generally 12.75 at rest (no load) and a low acceptance - i.e. they were not accepting a high charge rate of amps at the end of the charge cycle - indicates a fully charged battery. If the batteries reach 12.75 and the charging amps remain high the prime suspect s sulphated/old batteries.

BTW - You should only be seeing above 12.75 volts when chrging sources are active.

Batteries Don't Last Long Off Charge - If they seem to discharge quickly they are probably sulphated and capacity has erroded over time.

If you have either of these conditions I would replece the bank with AGM. GELS are more touchy in terms of charging and discharging than AGM. The gold standard is wet lead acid but most cruisers like the convenience of "maintenance free" AGM and so do I.

Charger - I don't know if noisiness is a reason to replace the charger but it could be good piece of mind to do so. I would do it after replacing the batteries. A common mistake people make is sizing the charger at 20 amps without cosidering house loads.

If the boat is naturally drawing 20 amps at the dock, there is no charging capacity left to charge the batteries. I was going to buy a 25 amp charger as the next step up was 40 in the model I wanted. A "deal" came along for the 40 and that's what I bought. I have no fears that standing boat load at the dock will ever exceed the capacity of the charger and there will be plenty of power to supply the boat loads and charge the batteries at the same time.
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Old 12-10-2014, 17:45   #7
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Re: Confused; Batteries/Chargers/etc.

12.65 is normal for a resting battery as far as what I've seen in the real world... including brand new marine batteries I had last year.
If the batteries in there lasted as long as you indicate... I wouldn't change a thing!!! (except the batteries)
Battery chargers get hot. If the batt's are charged it may not read above that level
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Old 14-10-2014, 06:07   #8
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Re: Confused; Batteries/Chargers/etc.

Quote:
Originally Posted by blinkerfluid View Post
Yes, 3 g31s for the house bank, 1 g27 for the starter.

In that case, whenever you eventually need to replace the house bank, and if you have the physical space... you might want to consider 4x deep cycle 6V golf cart batteries instead of the G31s. Size differences may just let you stuff 4x 6Vs into where you have 3x 12Vs now.

Do a search around here for threads about 6V golf cart batteries...

-Chris
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