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Discussion Starter · #1 ·
I have searched for similar thread but cannot find anything on this topic.

My boat (new to me) has two house banks, each T105s, one bank is new and the other is about 6 years old. The older bank is reported by a battery shop to be toast, but seems to run the system for 24hrs no problem with a little help from solar. The batteries are charges by an older Guest 50 amp charger. Arriving at the boat following a week of shorepower, both banks read 12.8 with no load. Application of 7 amps, (reefer/lights) and the system voltage drops to anywhere from 11.5 to 12.2. Remove this load and system voltage increases back to original value.
Is this normal? If so, and realising accurate battery voltage requires 24 rest period, how can I determine when each bank has reached 12.2 (50%) charge?
Next purchase is a smart charger and two more 105s. At that time I will leave the house battery switch on both to essentially have one bank of 450 ah (225 usable)
 

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I would replace the 6-year old T-105's without further ado. Then, I would run both banks as one single bank, giving you 450AH @ 20hr rate.

When fully charged and rested overnite with no load and no charge, you should measure 12.6-12.7V at the battery terminals (the only way to measure accurately in a new-to-you boat). Use a good digital multimeter, calibrated if possible.

For a new smart charger, I'd recommend you consider the Iota DLS series. They are IMHO the best value on the market today...well built, smart, reliable, and with a PWM charging technology which helps your batteries to last longer. They are a bargain at the discount prices offered by, e.g., Arizona Wind Sun. For your 450AH bank, I'd recommend the 75A model (DLS-75/IQ4).

New batteries need to be exercised a few times times (med-deep discharge followed by full charge) in order to reach their full capacity potential. If you have reason to believe they've been sitting awhile at the dealer's, it might be a good idea to equalize them, too.

Bill
 

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" Arriving at the boat following a week of shorepower, both banks read 12.8 with no load. Application of 7 amps, (reefer/lights) and the system voltage drops to anywhere from 11.5 to 12.2. Remove this load and system voltage increases back to original value.
Is this normal? "
For a dead battery bank, it is perfectly normal.

The float charge on good batteries should read about 13.6 when you get to the boat and drop to 12.6-12.7 when you knock down the float charge.

The fact that one of yours drops down to 12.2 means that bank is only holding a 60% charge, while the bank showing 11.5 volts is quite dead.

Doesn't matter what you can shake out of it--that bank is dead for any real load use. If you are charing both banks at the same time with the same controller, the dead bank might be the drain that is preventing the other bank from getting more than a 60% charge. GET RID OF IT.
 

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Discussion Starter · #4 ·
Thanks for the good advice.......however the question not addressed is what voltage should I expect to be reading on a fully charged, 225 ah batery bank with a 7amp constant load applied?
 

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7 amps is a small load for a T-105 bank of two 6V golf carts in series.

When the batteries are really "fully charged", you will see a float voltage for a short time...above 12.7VDC.

Thereafter, for quite a while, you should be seeing 12.6VDC. How long? Depends on several factors, some cited above.

If the batteries are in very good condition, have recently been exercised a few times, and have been fully charged at 14.4VDC, you'll see 12.6VDC for awhile. You may see 12.5VDC sooner than you'd think, but it will hang in there for a long time if only 7 amps is applied as a load.

There's no way to know the true capacity of your battery bank unless you do a constant load test, in this case applying about an 11 amp load for 20 hours, or until the bank reaches 10.5VDC.

By the way, voltages should be measured at the battery terminals with a calibrated digital voltmeter. You can't rely on other readouts, unless they are known to be accurate.

Bill
 

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Pior - system voltage (as this thread is called) is of fairly limited usefulness in determining the health and charge state of a battery bank. It's better than nothing, but a battery monitor will give you much better information.
 

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Nothing. without further information. Both are appropriate, depending on the situation. What's your question? What are the details of your setup? Why are you concerned?

Bill
 

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Hello: How much can one read into a float charge of 13.3 vice 13.6?
Well, I almost agree with BT, I'd say "nothing significant" rather than just nothing. In general, a lower float charge would indicate that your battery is weaker to begin with, or there are wiring losses higher than there should be, or the charging system isn't putting out as high a charge as it might/should be.

If the battery is load tested (or at least, tested with the float burned off and after allowing 24 hours for the chemistry to equalize internally) and the charging system is tested in operation, and both test out OK, then whatever the float charge measures, is normal for your setup.

13.3 versus 13.6 could just reflect the different between two meters. Rule of thumb, unless you have a recently calibrated high quality meter, is that the rightmost digit may be off by 2-3 numbers from meter to meter, and that's just because cheap meters aren't intended for high precision.
 

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I'd just stick with the plain old nothing. Without knowing if the batteries are wet, AGM, or gel and if the charger has a temp. sensor the 13.3 vs 13.6 means nothing at all.
 

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I asked because I know that my batteries are not up to snuff, but I don't know just how bad they are. We are hours away from the boat, so it's difficult to find the time to let the batteries come up to full charge then rest for 12/24 hours then let them drain at the recommended rate, etc. As I read the original statement as to float normally being at 13.6 I looked up and saw 13.3 on my link 2000R and wondered what sort of measure that might provide. I did notice a few days later after a sail and being plugged into the dock again, that the float again settled at 13.3.

The batteries are t-105s...four of them about five years old.

Thanks for the replies.

Bruce
 

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Does the charger have a temperature probe connected to the batteries?

If I lived hours from the boat I would have a mechanic stop by and do a load test. He will be able to see of the batteries behave normally under a load.

I'd say the float voltage has more to do with your charger than your batteries, unless they are really really bad.

Since you have a battery monitor you should be able to run the batteries down to 60% or so and then look at the voltage (after resting for a while). If the voltage is below what the tables say then your batteries are on their way out.
 

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Steve....
After a long weekend on the boat and re-reading the Heart 10 manual, the float (and accept) voltage is a function of temperature and what I was seeing was pretty much spot on according to their chart.

I did get to run a short load test....drawing 30% out of the batteries with a 5% load (440ah T-105s) stopping for short rest at 3 points. The voltage readings at those points were about 22 ah (5%) low. I had thought the batteries were in worse shape. Perhaps if I had had the time to go down to 60% I would have seen much worse performance?

Thanks, Bruce
 

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Based on the numbers you provided, I think your batteries are doing alright. Pulling them down a bit further and then waiting longer to look at the resting voltage would have been a more rigorous test. I'd just keep an eye on them at this point.
 
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