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Old 10-14-2020, 11:05 AM   #1
jeremyseattle
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Default The best article I've found about deep cycle batteries

I've been doing a lot of research, getting ready to install a new house battery bank. There are so many things to consider - Flooded vs. AGM vs. Lithium; 6V series vs. 12V parallel; manufacturers and brands; etc.

While doing all of this research, I found a lot of info about "Marine" and "RV" batteries and how their performance can really vary. I've also gotten advice from a lot of people about going with 6V golf cart batteries connected in series (coincidentally, this is the setup I already have - what came with my class C).

This article from marinehowto.com is the best I've found, explaining what "deep cycle" truly is - it breaks down the differences between true deep cycle batteries and those that are only labeled as such...

https://marinehowto.com/what-is-a-deep-cycle-battery/

It does not necessarily tell you whether 6V series or 12V parallel is better, but when you see the cross-section of the golf cart battery next to the "Marine deep cycle" one, you can see why so many people go with golf cart batteries. A true deep cycle 12V battery would probably perform as well as golf cart batteries, but you have to make sure you're getting true deep cycle.

For what it's worth, I haven't yet decided which way I'm going, but I'm leaning toward sticking with 6V in series, since I wouldn't have to change anything else. Well, I did order a replacement for my infamous Magnetek 6345 converter - orderd the PD 6300 kit (with 3-stage charger) from bestconverter.com - and I'll probably install a PowerPulse desulfator.

I think I'll buy the batteries directly from Dyno since I'm fortunate enough to be in Seattle, where they're made. The main hold-up is I'm still trying to find any data that tells me whether AGM is worth it - mainly for the deeper discharge tolerance...
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Old 10-14-2020, 01:13 PM   #2
Chuck v
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Jeremy,


That is a very good article you referenced and it is in full agreement with my experiences with DC systems in my off grid home (4 each L16 6v batteries in a series stack of 24 volts) and in my hunting camp trailer (2 each 6v GC batteries in series) and most recently in my diesel pusher coach where 4 each 6v GC batteries are wired in series/parallel as the inverter battery bank (this bank also is used to start the diesel generator...)


One thing that the article does not dwell upon is the charging challenges of lead acid batteries in parallel -- which is the underlying basis of all the admonitions that warn to only use exact match 12 volt batteries if connecting in parallel. These constraints are much more relaxed when charging in series.



When I was working in the solar industry, we delivered a shaved ice plant to the upper Nile valley to be used to ice down farmed perch in an area where there was no other refrigeration. These fish were an important protein source for the the locals across a wide area...so ice made them possible to transport by animal cart. The plant itself was solar powered (250 KW of panels) and the battery stack was 240 volts of very large 2volt lift truck cells in series. There were two such battery stacks that were alternated in their use -- but never charged in parallel. There were two back-up generators that were diesel powered and rated at 50 KW each. This was decades ago but the chemistry is unchanged on these flooded cell batteries.


As to AGM...these are less maintenance since you don't need to check for and add water periodically and they are not sensitive to tipping, but it is not justified in my mind for an RV use. My advice to you is get the golf car batteries and keep your original configuration.


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Old 10-14-2020, 01:19 PM   #3
jeremyseattle
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Thanks Chuck - I figured you'd be the first to chime in.

The ONLY reason I'm currently considering AGM is for deeper discharge - as you know from my previous thread, I'm wanting to keep my off-grid motor home warm when I'm away during cold winter nights, and 80% vs. 50% discharge would make a big difference. But we're also reconsidering our approach - might not leave it parked when the temps are going to be freezing - so that might be moot.

One question for you, Chuck: regarding charging in parallel - let's say I add two new 6V series batteries but want to keep my old ones - I guess I shouldn't hook them up in parallel with the new ones since they're not exact match?
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Old 10-14-2020, 01:37 PM   #4
Chuck v
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Jeremy,


If you look in the article about four each 6 volt GC batteries you will see how the cable connections should be made. It is still true that you need to have ALL batteries in the bank from the same manufacturer and with the same date code. The reason is the following:


When you charge flooded lead acid cells in parallel the least charged cell has the highest internal impedance, so it will absorb the least current if there is an alternate parallel path. In the best case this increases the time to achieve a full charge, and many cases badly matched batteries may not come anywhere close to achieving a full rated charge.


Conversely, in a series stack, this higher impedance causes a disproportionately larger voltage drop across this cell, so it will charge more than its neighbors until the charge state and voltage drops are balanced out and this results in the best charge outcome relative to recharge time.



Therefore, if you have the option, use cells with a higher amp-hr rating and connect them only in series to achieve the system voltage you are desiring. This is why the off-grid home I had used L16 batteries just in series, and not GC batteries in series/parallel. Those L16 batteries had a service life of more than 10 years. Of course, I had plenty of height for these L16 batteries, you would not likely have space for any of these in a motor home. and they are a beast to maneuver around since they weigh almost 120 pounds each!!


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Old 10-14-2020, 06:04 PM   #5
jeremyseattle
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Makes sense - thanks again Chuck!
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