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Old 03-08-2014, 03:26   #1
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Battery gets Hot but not Full

I just noticed that my 30 Amp shore power charger is still putting full 30 Amps to batteries after 7 hours of charging and the bank voltage is only 12.7 V. That's definately not normal so I turned the charger off and opened the battery bank. I have two 135 Ah leisure batteries next to each other and the other battery was almost too hot to touch!

The batteries are Bosch flooded wet cell batteries. It says maintenance free on top of the battery but there are still caps where I can check and refill the water level.

Obviously the batteries needs to be changed but any ideas what caused the problem?
- The batteries are less than a year old
- They have been only twice below 12.0 V and those times only 11.7 V so not completely empty
- Both batteries had their plates covered with water
- Voltage after disconnecting and few hours of cooling was 12.5 V

Can the batteries be short-circuited since the voltage is still 12.5 volts? Or what could be the problem? Is it likely that the root cause is somewhere else than in the batteries, i.e. it's not enough to change the batteries?

Any comments and help is appreciated!

Sam
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Old 03-08-2014, 04:02   #2
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Re: Battery gets hot but not full

How do you know it was charging at 30 amps? What was the voltage on the batts while charging? Were any house loads on while charging?

I would remove the hot battery from the bank, discharge the remaining battery isolate boats' bus ensuring no house loads and monitor what is happening while the "good" battery is getting charged.

If the charger was really pushing 30 amps after 7 hours something is seriously wrong with the batteries or the charger. The hot battery does indicate a shorted battery to me. This could be caused by how the battery was used over the last year or just a random (it happens) battery failure.
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Old 03-08-2014, 05:06   #3
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Re: Battery gets hot but not full

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How do you know it was charging at 30 amps? What was the voltage on the batts while charging? Were any house loads on while charging?

The meter in the charger shower 30 amps all the time. I also have a shunt in the minus pole of the battery to measure the current flow which was about 22 amps all the time. The difference comes from the fridge which took the 8 amps. The voltage while charging was 12.7 V which is lower than usual.
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Old 03-08-2014, 05:06   #4
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Re: Battery gets hot but not full

The hot battery is sulphated. A layer of sulphate has settled at the bottom and built up high enough to short the plates which draws current ahd heats the battery. That is a good indication that your batteries were thin plate starting batteries (with less space for sulphate to accumulate).

There are few real deep cycle 12V batteries. Most are labeled dual purpose, but are not. Replace both with two 6V golf cart batteries wired in parallel to give 12V. They should last at least 5 years.

Also after replacing, make sure that your charger comes up to 14+V on its acceptance cycle and drops to the mid 13s for float.

David
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Old 03-08-2014, 06:34   #5
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Re: Battery gets hot but not full

I found "nearly new" batteries misbehave after they got deeply discharged at a point and left sitting like that for any time. I think this is where sulphation gets them.

Something sounds odd in your voltage/amperage monitoring system too. Most chargers have a cut-off point and will not put out max amps over 7 hours!

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Old 03-08-2014, 07:43   #6
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Re: Battery gets hot but not full

is the charger reliable? maybe it freaked out somewhere along the line. a power surge or sensor problem in the circuit? 30 amps for 7 hours would definitely heat up a battery.
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Old 03-08-2014, 07:57   #7
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Re: Battery gets hot but not full

The battery is Bosch T3 which, I suppose, is a wrong choice for a leisure battery. The batteries were purchased this spring just before I bought the boat, so I know the history of the batteries. The lowest voltage has been 11.7 V and I assume that should not destroy the battery and cause sulfation even if the battery is thin plated start battery. Or am I completely wrong here?

My charger is Victron Centaur charger 12V/30amp. I don't know if it has a protection for not charging 30 amps over certain time. However, if my battery bank would be slightly bigger and 60% used then 7 hour charging with full amps would be normal so I don't know whether there should be that kind of protection.
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Old 03-08-2014, 08:01   #8
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Re: Battery gets hot but not full

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The hot battery is sulphated. A layer of sulphate has settled at the bottom and built up high enough to short the plates which draws current ahd heats the battery. That is a good indication that your batteries were thin plate starting batteries (with less space for sulphate to accumulate).

There are few real deep cycle 12V batteries. Most are labeled dual purpose, but are not. Replace both with two 6V golf cart batteries wired in parallel to give 12V. They should last at least 5 years.

Also after replacing, make sure that your charger comes up to 14+V on its acceptance cycle and drops to the mid 13s for float.

David

Thanks for the comments David! Do you have any ideas why my battery was sulphated even though it hasn't been under 11.7 V and is only half a year old?

Golf cart batteries sounds good. How many amp hours they are usually and is there certain brands I should favor or avoid? And any ideas where I could get those in Greece? Probably not from standard marine stores?
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Old 03-08-2014, 08:04   #9
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Re: Battery gets hot but not full

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Originally Posted by gonesail View Post
is the charger reliable? maybe it freaked out somewhere along the line. a power surge or sensor problem in the circuit? 30 amps for 7 hours would definitely heat up a battery.
For a given voltage the amount of current is determined by the battery and its state of charge. He states the voltage never went above 12.7 volts. A good battery would not accept that much current when charged, so there must be a bad battery or a short. (The short probably being in the battery itself.)
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Old 03-08-2014, 08:34   #10
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Re: Battery gets hot but not full

Quote:
Originally Posted by Sam the Sailor View Post
The battery is Bosch T3 which, I suppose, is a wrong choice for a leisure battery. The batteries were purchased this spring just before I bought the boat, so I know the history of the batteries. The lowest voltage has been 11.7 V and I assume that should not destroy the battery and cause sulfation even if the battery is thin plated start battery. Or am I completely wrong here?

My charger is Victron Centaur charger 12V/30amp. I don't know if it has a protection for not charging 30 amps over certain time. However, if my battery bank would be slightly bigger and 60% used then 7 hour charging with full amps would be normal so I don't know whether there should be that kind of protection.
It was a bit difficult to find specs for the T3 battery but Bosch makes many models of the T3 with different capacities. It looks like the bottom end of their truck/commercial batteries and appears to be a start battery.

This is probably not the battery to be using on a boat for house loads but on a power boats it may be suitable especially if the engine is running a lot.

11.7 is actually a pretty deep cycle and could indicate 70% discharge batteries definitely don't like that.

If you plan to be engine off and drawing down the current frequently you definitely need to consider a deep cycle battery solution.
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Old 03-08-2014, 08:45   #11
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Re: Battery gets hot but not full

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Originally Posted by djmarchand View Post
The hot battery is sulphated. A layer of sulphate has settled at the bottom and built up high enough to short the plates which draws current ahd heats the battery. That is a good indication that your batteries were thin plate starting batteries (with less space for sulphate to accumulate).

There are few real deep cycle 12V batteries. Most are labeled dual purpose, but are not. Replace both with two 6V golf cart batteries wired in parallel to give 12V. They should last at least 5 years.

Also after replacing, make sure that your charger comes up to 14+V on its acceptance cycle and drops to the mid 13s for float.

David
Oooohhh nooooo!!! Wire them in series to get 12V.

Mainesail has recommended EGC2 from Sam's Club in his past postings. I took his advice and installed two last spring (210AH if I remember correctly...maybe 215) and they have performed well. About a hundred bucks each.

One 30W solar panel keeps them topped up (the engine alternator runs a couple of hours a month while leaving the slip and returning and also alongside when needed for PM).
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Old 03-08-2014, 08:57   #12
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Re: Battery gets hot but not full

This has all the characteristics of a shorted cell. As with any product, a small number of batteries fail because of manufacturing errors that weren't caught during factory QA. The fact that the other battery that was bought at the same time appears fine is another indication. Even the best deep cycle brands have occasional bad apples.

This is why batteries have warranties. Unfortunately yours may have lapsed as it is over a year. Manufacturers will sometimes replace a recently out of warranty battery if they determine that it was a manufacturing error or just for customer goodwill. I'd ask.
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Old 03-08-2014, 08:57   #13
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Re: Battery gets hot but not full

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It was a bit difficult to find specs for the T3 battery but Bosch makes many models of the T3 with different capacities. It looks like the bottom end of their truck/commercial batteries and appears to be a start battery.

This is probably not the battery to be using on a boat for house loads but on a power boats it may be suitable especially if the engine is running a lot.

11.7 is actually a pretty deep cycle and could indicate 70% discharge batteries definitely don't like that.

If you plan to be engine off and drawing down the current frequently you definitely need to consider a deep cycle battery solution.

I have a sailing boat so I'm indeed drawing down the current frequently. Thus the deep cycle golf cart batteries should be a good alternative to replace the current batteries.

Yes 11.7 V is quite deep cycle but my understanding is that even start batteries should withstand two short perioids of 11.7 V without short-circuiting if they are above 12.0 V the rest of the time.
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Old 03-08-2014, 09:16   #14
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Re: Battery gets hot but not full

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Originally Posted by Sam the Sailor View Post
I have a sailing boat so I'm indeed drawing down the current frequently. Thus the deep cycle golf cart batteries should be a good alternative to replace the current batteries.

Yes 11.7 V is quite deep cycle but my understanding is that even start batteries should withstand two short perioids of 11.7 V without short-circuiting if they are above 12.0 V the rest of the time.
It all depends on what you mean by 'short period'. If you leave a LA battery at 11.7 for more than overnight, you are asking for significant sulfation. The description of your batteries does indicate a shorted cell in the one which got hot. If you want to bother, you can stick a probe wire in the liquid of each cell and measure the voltage in the individual cells.
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Old 03-08-2014, 09:23   #15
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Re: Battery gets hot but not full

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It all depends on what you mean by 'short period'. If you leave a LA battery at 11.7 for more than overnight, you are asking for significant sulfation. The description of your batteries does indicate a shorted cell in the one which got hot. If you want to bother, you can stick a probe wire in the liquid of each cell and measure the voltage in the individual cells.

The short period meant about day and a half so maybe that was the reason. However, I'm a bit surprised that the batteries are so vulnerable. What would be your advice in the future regarding lowest voltage? Never let under 12.0 V to avoid problems?

If the battery is shorted what should I expect the total voltage over the battery be? And should I measure the voltage between liquid and minus pole of the battery?
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