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Old 01-20-2017, 03:33 PM   #1
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Batteries again...6V vs 12V..??

Greetings folks,
Making the dangerous assumption that most if not all modern RVs use 12V systems, I am puzzled by the frequent discussions of 6V batteries. Question is; is there anything inherently better about using four 6V batteries in series-parallel over four 12V batteries all in parallel? My Merchant Marine background argues that with four 12V batteries you can lose one bad one and still have 75% of your 12V capacity. Lose one 6V battery and you are down to 50% capacity. That one still good 6Ver is useless without it's partner.
That as I see it is the bad side of using 6V batteries. Can someone please show me the good side of using the 6V batteries?
Chuck Peck in CasaLoca
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Old 01-20-2017, 04:12 PM   #2
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I think it's only about available aH.
6 volt golf cart batteries are readily available
and hold a lot of aH....more than the average hybrid type marine/rv battery

Trojan 6V cart battery T-105 holds 225aH at teh 20 hour rate, so a bank of two would be 450aH, right?

Trojan 12 V T-1275 is 150aH in a slightly larger and heaver box, so a bank of two would be only 300aH.... and perhaps a bit less available

the hybrid marine type boat/rv batteries hold much less still
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Old 01-20-2017, 05:18 PM   #3
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Quote:
rojan 6V cart battery T-105 holds 225aH at teh 20 hour rate, so a bank of two would be 450aH, right?
Is the 225aH at 6 Volts? If so I think its equivalent to 117 aH for a 12 V battery.
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Old 01-20-2017, 08:14 PM   #4
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Originally Posted by Cosmo View Post
Is the 225aH at 6 Volts? If so I think its equivalent to 117 aH for a 12 V battery.
Yes, I think you are on to the problem there. It has been a long time since I studied electricity but I don't think you can double BOTH values. With two batteries of 6V and 225 amphours, you can wire to get 225 amphours at 12V
OR you can wire to get 450 amphours at 6V. I just don't think those two batteries can put out 450 amphours at 12V.
Am I wrong and we just threw Mr. Watt out the window?
Chuck Peck in CasaLoca
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Old 01-20-2017, 08:24 PM   #5
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Originally Posted by CasaLoca View Post
Yes, I think you are on to the problem there. It has been a long time since I studied electricity but I don't think you can double BOTH values. With two batteries of 6V and 225 amphours, you can wire to get 225 amphours at 12V
OR you can wire to get 450 amphours at 6V. I just don't think those two batteries can put out 450 amphours at 12V.
Am I wrong and we just threw Mr. Watt out the window?
Chuck Peck in CasaLoca
Correct - Connecting batteries you can EITHER double the VOLTAGE (series) or AMPERAGE (parallel) - but not both.... 1+1 doesn't equal 4...

You can get 6V at 450AH or 12V at 225AH from those 2 batteries.
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Old 01-20-2017, 08:31 PM   #6
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you're right, I wasn't thinking straight.....
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Old 01-20-2017, 08:34 PM   #7
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I'm thinking the big advantage then for 6V might be the availability.
If you want a true deep cycle golf cart type battery, it's probably easier to find 6 volt over a 12 volt
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Old 01-20-2017, 08:38 PM   #8
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Back to the original question of why 6v.. (and I use 12v currently)
But as I understand - the available 6V batteries have thicker plates and are more intended for and tolerant of deep discharge than what we have available for 12v... No reason 12v couldn't - just not made the same (would likely add to size/weight...)

To me first step is determine your battery capacity needs - then find the best combination (size, voltage, cost) that meets your needs..
It might be a 6v solution in series (and parallel if more than 2)... might be 12v in parallel...
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Old 01-21-2017, 04:58 AM   #9
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One advantage is having fewer and larger battery cells. We must have 6 as a minimum, so why go with 24 when 12 works well?
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Old 01-21-2017, 06:06 PM   #10
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Originally Posted by CasaLoca View Post
... Can someone please show me the good side of using the 6V batteries
This has historically been simply supply and demand. The 6V GC battery format is/was the most readily available highest cell capacity at the lowest cost for many years.

Two good 6V deep cycle batteries with about 225AH@20hr rate can be purchased for around $160-300 while the same 12V single battery equivalent has been at a 30%+ price premium and difficult to find.

A today example of a 12V near apples to apples comparison with 2x6V series batteries is the Trojan J185H and 2xT105 (plus jumper cable). With internet availability and end prices nearly equal, the single 12V J185H is technically the better choice though in real life it wouldn't likely matter enough to measure. Will the form factor fit and can you handle a single 130lb J185H battery?

Current summary is that it is getting harder to justify using 6V GC batteries for 12V service.
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Old 01-21-2017, 07:14 PM   #11
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My golf cart uses 4 12v trojan 1275plus batteries.
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Old 01-21-2017, 07:43 PM   #12
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This has historically been simply supply and demand. The 6V GC battery format is/was the most readily available highest cell capacity at the lowest cost for many years.

Two good 6V deep cycle batteries with about 225AH@20hr rate can be purchased for around $160-300 while the same 12V single battery equivalent has been at a 30%+ price premium and difficult to find.

A today example of a 12V near apples to apples comparison with 2x6V series batteries is the Trojan J185H and 2xT105 (plus jumper cable). With internet availability and end prices nearly equal, the single 12V J185H is technically the better choice though in real life it wouldn't likely matter enough to measure. Will the form factor fit and can you handle a single 130lb J185H battery?

Current summary is that it is getting harder to justify using 6V GC batteries for 12V service.
Great battery comparison. Those batteries do compare almost exactly the same right down to Amp-hours, energy storage, weight and projected 1,200 cycles at 50%. I happen to have picked up Trojan catalogs yesterday at Tampa show.

Do you happen to know how these choices compare in cost?
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Old 01-21-2017, 07:50 PM   #13
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The problem for those of us with smaller motor homes like the Axis is battery size. The Trojan 12v is 14.7" high and the 6v is 11.1" high - both higher than the max 10" my battery box will hold. I don't think I can fit two 6v batteries in my Axis. Has anyone ever tried? It might depend on the placement of the terminals.
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Old 01-21-2017, 08:48 PM   #14
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Originally Posted by Chance View Post
Great battery comparison. Those batteries do compare almost exactly the same right down to Amp-hours, energy storage, weight and projected 1,200 cycles at 50%. I happen to have picked up Trojan catalogs yesterday at Tampa show.

Do you happen to know how these choices compare in cost?
Roughly the same depending on where you source them.
J185H-AC is $306 and a T105 is $162 at The Solar Biz Better pricing can be found for the T105 though their price on the 12V caught my attention.

Quote:
Originally Posted by Oneilkeys View Post
The problem for those of us with smaller motor homes like the Axis is battery size. The Trojan 12v is 14.7" high and the 6v is 11.1" high - both higher than the max 10" my battery box will hold. I don't think I can fit two 6v batteries in my Axis. Has anyone ever tried? It might depend on the placement of the terminals.
Not many choices for the Axis/Vegas battery compartment for sure! I was going to swap out the GC batteries from our previous RV and discovered they were just a bit too tall. Only option I've found is lithium and I'm having a difficult time justifying the expense.
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Old 01-21-2017, 09:21 PM   #15
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Originally Posted by Oneilkeys View Post
The problem for those of us with smaller motor homes like the Axis is battery size. The Trojan 12v is 14.7" high and the 6v is 11.1" high - both higher than the max 10" my battery box will hold. I don't think I can fit two 6v batteries in my Axis. Has anyone ever tried? It might depend on the placement of the terminals.




Quote:
Originally Posted by TyCreek View Post
Roughly the same depending on where you source them.
J185H-AC is $306 and a T105 is $162 at The Solar Biz Better pricing can be found for the T105 though their price on the 12V caught my attention.



Not many choices for the Axis/Vegas battery compartment for sure! I was going to swap out the GC batteries from our previous RV and discovered they were just a bit too tall. Only option I've found is lithium and I'm having a difficult time justifying the expense.

The Trojan battery catalog shows various 12-Volt AGM batteries that are under 10 inches high. I'm guessing you prefer flooded but if considering lithium, perhaps AGMs are not out of question.

For what it's worth, the Trojan representatives at Tampa show said they would have an expanded line of AGMs starting in June, which will include tall batteries like L16 size. They are not looking at lithium technology at present (according to reps), but I think they may be expanding AGM lines to better compete with lithium.


Ty, thanks for pricing information. That's a good price for a large 3 kW-hr battery.
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Old 01-22-2017, 01:08 AM   #16
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AGM energy density is slightly less but similar to FLA so capacity that will fit in the Axis step remains the same. The benefits I see with AGM for RV use is less maintenance, faster charge and maybe a bit more DOD assuming a proper charging system (not the factory installed charger).

The cost of AGM would have to drop considerably to compete because Lithium has already reached similar or better cost points for power storage.

This lithium battery example shows 15% less cost to provide the same projected energy @1000 cycles:
$360 for TROJAN 31-AGM 12V 100AH provides >500 80% DOD cycles
$615 for LiFeMnPO4 Prismatic 12.8V 100Ah provides >1000 80% DOD cycles

EDIT: I just noticed that the link I gave was $100 less than I had in my spreadsheet from previous 100AH AGM lookup that I used for calculation. So, my example statement is WRONG! It's back to AGM pulling into the lead again for being more cost effective. The point however is that lithium is quickly eliminating reasons for advancing lead acid battery solutions in any configuration AGM/GEL/FLA.
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Old 01-22-2017, 02:53 AM   #17
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Two AGMs might just fit in my Axis battery box. They are 1.5" longer (total) than my two 29's - that just fit. I had AGMs in my sailboats for years and they were really good. But I installed an 80 amp alternator which significantly shortened my charging times. I might just try them when I need to replace my current batteries. However, they are three and a half times as expensive as the size 29 batteries I have now, and I would have to be committed to keeping my current RV go for a good long time for it to be worthwhile.
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Old 01-22-2017, 02:49 PM   #18
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In the Trojan catalog, they list AGMs at 1,000 cycles at 50% DOD, whereas most models in their flooded Signature Line are rated at 1,200 cycles at 50% discharge. A few sizes in Signature Line only receive a 600 cycle rating at 50% DOD (may want to avoid those). For Trojan brand, it doesn't appear AGMs would last longer.

Prices on these Trojan AGMs seem to run around 50% higher than equivalent-capacity flooded; although at +/- $200 per kWh it's still much cheaper than lithium "retail" prices.

The main reason I have looked at AGMs is to either place them inside the RV, or to place them under the floor where battery access for watering flooded batteries isn't practical.
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Old 01-22-2017, 03:07 PM   #19
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Hmm they are coming down: This guy is pretty attractive at $899:
https://battlebornbatteries.com/

This one is a little bit more: $1299 for 100Ah
http://www.lithiumion-batteries.com/...m-ion-battery/
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Old 01-22-2017, 03:51 PM   #20
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Originally Posted by JamieGeek View Post
Hmm they are coming down: This guy is pretty attractive at $899:
https://battlebornbatteries.com/

This one is a little bit more: $1299 for 100Ah
12V 100AH Lithium Ion Battery | Lithium Ion Battery | Deep Cycle | Starting
Agree the price is better than Smart Battery, although still expensive on a kWh basis unless you factor the longer cycle life. And that's where it gets a little complicated for me.

On the lead acid side of cost estimate, he only uses 300 cycles at 50% DOD, whereas Trojan estimates 1,200 at same 50% DOD. He also uses $450 cost for 200 Amp-hour capacity which should be closer to $300 -- unless he's comparing against AGMs and not flooded.

The other issue for me is that lithium cost is based on 3,000 cycles at 100% DOD, and even if the battery was capable of that, the motorhome would likely see the graveyard much before that. You'd have to fully discharge the battery every day for 10 years to get that level of economy.

Regardless of some exaggeration, if it's close in lifetime costs, then the weight difference and faster charging alone would make it worthwhile. It's still a big initial-cost hit if you buy a couple of these 100-Ah batteries. On the other hand what's another $2,000 when buying a $100,000 motorhome?
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