Adding Coach batteries

[Metalman]

I would like to see the curves and I would also like to see the difference in charge/discharge comparisons between deep cycle flooded lead acid batteries and deep cycle AGM batteries.

[Ag&Au]

These analyses are all true for the most part, but there are so many different circumstances that it seems silly to me, to try to come up with "you can or should always" rules for battery use. My simple procedure is to have a volt meter installed in the system somewhere so I can see what the batteries are doing. I always try to charge them at every opportunity. If the voltage starts to drop to what I consider to be a low level (that varies with circumstance), I make a point of charging them again. I always install an quality convertor that has an intelligent charging control scheme.

The rest of the equation is to buy batteries appropriate to your useage and seek advice from a qualified battery specialist if you are uncertain.

To me the most important parts of all this is:
Always have a voltmeter to monitor the batteries.
Always be sure you have a top end converter(seldom found in new RVs) that is designed to keep the batteries operating at their peak.

Ken

[Chance]

Originally Posted by Metalman

I would like to see the curves and I would also like to see the difference in charge/discharge comparisons between deep cycle flooded lead acid batteries and deep cycle AGM batteries.

Basic curves look like this. This one happens to be from Lifeline. The magnitude of values may be different, but the shape of the curve will be similar for same type of battery.

[Metalman]

Is that graph for a deep cycle lead acid flooded battery? Interesting that they discharge the battery to 10.5 volts. If the 10.5 volts is not under a moderate load, it's lower than most RVers would let their batteries discharge.

[Ag&Au]

Originally Posted by Metalman

Is that graph for a deep cycle lead acid flooded battery? Interesting that they discharge the battery to 10.5 volts. If the 10.5 volts is not under a moderate load, it's lower than most RVers would let their batteries discharge.

I am curious how you arrived at 10.5 volts. The chart is showing how many charge/discharge cycles to expect for different depths of discharge. My perception is that for the extreme case of 100% it would be 0 volts and of course some other calculable value at other percentages. So each point of the chart is going to be different voltage at discharge.

The other factor is that Lifeline batteries are AGM batteries and thus preform somewhat differently than regular lead plate batteries. I'm guessing that this graph would show significant shorter number of cycles life towards the right (higher percentage of discharge) side if it were for non-AGM batteries. These are my opinions not to be confused with facts.

https://www.solar-electric.com/agm-b...echnology.html

Ken

[Chance]

Originally Posted by Ag&Au

I am curious how you arrived at 10.5 volts. The chart is showing how many charge/discharge cycles to expect for different depths of discharge. My perception is that for the extreme case of 100% it would be 0 volts and of course some other calculable value at other percentages. So each point of the chart is going to be different voltage at discharge.

The other factor is that Lifeline batteries are AGM batteries and thus preform somewhat differently than regular lead plate batteries. I'm guessing that this graph would show significant shorter number of cycles life towards the right (higher percentage of discharge) side if it were for non-AGM batteries. These are my opinions not to be confused with facts.

https://www.solar-electric.com/agm-b...echnology.html

Ken

Ken, one of the notes at bottom of chart shows 1.75 Volts per cell, which works out to 10.5 Volts for a 6-cell 12-Volt battery.



By the way, I would have to go back and read the entire report again since it's been a couple of years, but I believe that discharge tests were done at different levels of energy based on new-battery condition representing 100% capacity. It then gets done over and over until battery can no longer hold at least 1.75 Volts at end of final test cycle.

As an example, say the battery has 1.5 kW-hr of rated energy at 20-hour discharge rate. If I recall correctly, the 50% depth of discharge would then drain 50% of 1.5 kW-hr out of battery. They would do this over and over again until after the last cycle, in this case 1,000 cycles, the battery can't hold the minimum of 10.5 Volts (for 12-volt battery) to be considered usable.

I'm not 100% sure of details so I could be wrong. I'm sure this test information can be found by doing a search.

[Ag&Au]

Originally Posted by Chance

Ken, one of the notes at bottom of chart shows 1.75 Volts per cell, which works out to 10.5 Volts for a 6-cell 12-Volt battery.


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I'm not 100% sure of details so I could be wrong. I'm sure this test information can be found by doing a search.

Thanks for the explanation. I do great with 'rithmatic, but reading bores me quickly.

What is confusing to me is they say "charge voltage and discharge voltage" not charged and discharged. That leads me to believe that they charged with a charger outputing 14.4 volts and discharged it with a load that drew enough current to drop the output voltage to 10.5.

Once again proving English is a weird and complicated language.

I would certainly expect them to measure the percent of discharge by measuring the specific gravity of the electrolyte.


Ken

[Metalman]

Ken, Chance,
Thanks for the info. on AGM batteries. The graph and the link to the web site are both helpful. I have been using AGM batteries in my motorcycles for several years and haven't had a failure yet. The fact that they don't need maintenance, are vibration resistant, and have a slow discharge rate when not being used are excellent characteristics and worth the difference in cost to me.

The cost of the AGM deep cycle batteries that I recently installed in the RV were about three times the cost of a group 27 deep cycle battery. They came with knurled brass posts, so I had to buy adapters for the screw connections. The are now disconnected from the coach and connected to a battery maintainer, since the coach is being stored.

[Ag&Au]

Originally Posted by Metalman

Ken, Chance,
Thanks for the info. on AGM batteries. The graph and the link to the web site are both helpful. I have been using AGM batteries in my motorcycles for several years and haven't had a failure yet. The fact that they don't need maintenance, are vibration resistant, and have a slow discharge rate when not being used are excellent characteristics and worth the difference in cost to me.

The cost of the AGM deep cycle batteries that I recently installed in the RV were about three times the cost of a group 27 deep cycle battery. They came with knurled brass posts, so I had to buy adapters for the screw connections. The are now disconnected from the coach and connected to a battery maintainer, since the coach is being stored.

I posted elsewhere here, maybe even in this thread, but I think it bears retelling. My travel trailer came from the factory with 2 group 27 Lifelines.

I nearly always had the trailer plugged into shore power when stored. As soon as I received the trailer from the dealer, I replaced the converter with an IOTA DLS/IQ-4.

I sold the trailer 7 years later and the batteries' performance had not decreased at all.


Ken

[Metalman]

Ken,
Yes I read that earlier. Because I am not sure what I have for a converter I am not leaving the batteries connected to the coach, even when the store/use switch is in the store position. I suspect that then batteries over charged because three of the twelve cells were very low on electrolyte after being left plugged in for a few months. Yes, I should have checked them more often. Also the batteries were boiling and too hot to touch. The sides were swollen on one, indicating that it had sulfated. I expect to replace the engine battery sometime soon. I will replace it with a maintenance free battery.

[Chance]

Originally Posted by Ag&Au

....cut...

I would certainly expect them to measure the percent of discharge by measuring the specific gravity of the electrolyte.


Ken

I would not.

In this case I wouldn't expect it to give you the same results at beginning of test versus end of test -- not if I recall test correctly. At beginning of test (discharge cycle #1) the battery is taken down to 50% (using the same example I used previously) but at discharge cycle #1,000, the battery is taken down to 10.5 Volts, or all the battery can do. I'd expect different SG under those conditions.

[Ag&Au]

Originally Posted by Chance

I would not.

In this case I wouldn't expect it to give you the same results at beginning of test versus end of test -- not if I recall test correctly. At beginning of test (discharge cycle #1) the battery is taken down to 50% (using the same example I used previously) but at discharge cycle #1,000, the battery is taken down to 10.5 Volts, or all the battery can do. I'd expect different SG under those conditions.

Do you happen to have the link to the explanation of the test? I am getting confused. I have always thought that SG was the best test for battery charge % as long as it was given a chance to stabilize. I guess I need to do more reading.

Ken

[Chance]

Originally Posted by Ag&Au

Do you happen to have the link to the explanation of the test? I am getting confused. I have always thought that SG was the best test for battery charge % as long as it was given a chance to stabilize. I guess I need to do more reading.

Ken

I tried to open my saved link yesterday and it gave me an error message.

I did a quick search and found other references that may help, although this one doesn't go into test details. It covers it by definition.

Battery Life and How To Improve It

"Some applications such as electric vehicles or marine use may require the maximum capacity to be extracted from the battery which means discharging the battery to a very high DOD. Special "deep cycle" battery constructions must be used for such applications since deep discharging may damage general purpose batteries. In particular, typical automotive SLI batteries are only designed to work down to 50% DOD, whereas traction batteries may work down to 80% to 100% DOD."

[Ag&Au]

Originally Posted by Chance

I tried to open my saved link yesterday and it gave me an error message.

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Battery Life and How To Improve It
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Thanks

Ken