Pros & Cons of 12 volt vs 6 volt batteries

[deckofficer]

Originally Posted by exMaggieDrum

My misunderstanding I guess. But 2v cells are just a different way to "package" the same capacity, but with even more "batteries", but perhaps with ready-made external intercell connections. There's still no free lunch here.

Well not quite. Thicker plates for more cycles, and for a given form size 3 times the ahr of a 6 volt battery. Of course 3 times the number of batteries, but all in series. If 220 ahr meets your needs (2640 whr) then two 6 volt golf cart batteries. If your back can tolerate moving a 115 lb battery, the L16 case size will give 370 ahr (4440 whr) for two 6 volt batteries. But if you need more storage, then 2 volt cells make sense. (6) L16 2 volt cells in series give 1,100 ahr (13.2 kwhr).

[ramblinrod]

Originally Posted by deckofficer

Well not quite. Thicker plates for more cycles, and for a given form size 3 times the ahr of a 6 volt battery. Of course 3 times the number of batteries, but all in series. If 220 ahr meets your needs (2640 whr) then two 6 volt golf cart batteries. If your back can tolerate moving a 115 lb battery, the L16 case size will give 370 ahr (4440 whr) for two 6 volt batteries. But if you need more storage, then 2 volt cells make sense. (6) L16 2 volt cells in series give 1,100 ahr (13.2 kwhr).

No free lunch.

With your 2 volt battery configuration, if one battery goes down, you got nada.

You can't jumper the bad battery, as many boat devices won't work on just 10 volts. Your alternator would just love this too.

Whereas, if you had 10 x Grp 27 115 Ahr batteries in parallel, and one bit the dust, you isolate it and still have 12 volts with 1035 Ahrs of capacity, (just a 10% reduction instead of 100% reduction.

So the 2 Vdc battery system has some advantages, but a battery failure is catastrophic to the system, rendering the whole thing useless until the dud battery is replaced.

[valhalla360]

Originally Posted by jeepbluetj

6v golf cart batteries generally have much thicker plates than their 12v "deep cycle" counterparts. i.e. the 6v battery is truly a deep cycle battery where most of the 12v batteries are dual-purpose.

They're also relatively cheap. They're also much easier to handle than 4d or 8d batteries. Bang-for-buck, for a SLA, I'd _always_ go for 6v batteries.

Search this forum, any RV forum, you'll find plenty of responses on this specific question.

All the talk about wiring differences is negligible. Assuming you wire it up properly and keep the connections clean, it's just not worth concerning yourself over.

Likewise, reliability is not so much about more parts it's about the thicker plates. Again assuming you don't abuse them, it's not a big concern and the ability to isolate a bad 12v battery in a two battery bank is a big advantage if you are away from an easy replacement.

The real issue is 6v batteries are almost exclusively used for deep cycle use so they are built for deep cycle use (mostly thicker plates). The biggest user is golf courses and they often buy them by the dozen and use them hard. If one brand doesn't hold up, it's quickly obvious and they would be pushed out of the market.

The vast majority of 12v batteries are designed for starting with some labled combination or deep cycle without really changing much other than the lable. Most get used in bass boats and similar situations where the owner buys one and it sits for weeks or months on end. Most failures are chaulked up to abuse and only buying 1 battery every 2-4yrs, they don't get a good feel for the statistical difference. End result is there is little incentive for manufacturers to mass produce true deep cycle 12v batteries.

[jwcolby54]

Originally Posted by deckofficer

If your back can tolerate moving a 115 lb battery, the L16 case size will give 370 ahr (4440 whr) for two 6 volt batteries. But if you need more storage, then 2 volt cells make sense. (6) L16 2 volt cells in series give 1,100 ahr (13.2 kwhr).

the ideal place to do this on my boat would be all the way at the back against stern wall. There's a lot of room back there under the cockpit and the seats have hatches which lifts up, which would allow me to use ropes and pulleys to get the batteries down in there.

But 700 pounds feels like a lot of weight to put that far back on a 33 foot 14000 pound boat.

[roverhi]

There are remote fill options for FLA batteries. They replace the caps on the batteries and have tubing that delivers fluid to all the cells and the caps shut the flow off when the cell is topped off. There is a single point refill connection and use a squeeze tube to add water. Just squeeze the bulb until you get back pressure and the batteries are topped off. Two of my four house batteries are buried under the settee. Used to have to pull them out to check and fill them now just hook up the bulb pump and squeeze.

[jcapo]

Originally Posted by roverhi

Two of my four house batteries are buried under the settee. Used to have to pull them out to check and fill them now just hook up the bulb pump and squeeze.

Which fill system are you using? Any problems?

[deckofficer]

Originally Posted by ramblinrod

No free lunch.

With your 2 volt battery configuration, if one battery goes down, you got nada.

You can't jumper the bad battery, as many boat devices won't work on just 10 volts. Your alternator would just love this too.

Whereas, if you had 10 x Grp 27 115 Ahr batteries in parallel, and one bit the dust, you isolate it and still have 12 volts with 1035 Ahrs of capacity, (just a 10% reduction instead of 100% reduction.

So the 2 Vdc battery system has some advantages, but a battery failure is catastrophic to the system, rendering the whole thing useless until the dud battery is replaced.

I use LiFePO4, so never need to deal with batteries again. But if using flooded lead acid for deep cycle applications you want as thick a plates as possible and that would be 2 volt cells. So instead of (10) group 27s, go with two banks of (6) 2 volt cells. Should you have a very unlikely cell failure, you still have the 2nd bank. Sure that cuts the capacity by 1/2 but the life span is far superior with the 2 volt cells, not to mention a single series string is much better than a few weak cells in all those parallel cells always pulling the entire bank down.

[roverhi]

Originally Posted by jcapo

Which fill system are you using? Any problems?

Using this system: Battery Watering Technologies - FLOW-RITE Battery Watering Systems - PRO-FILL Battery Watering - QWIK-FILL - Powerstride Battery.com - Call 877-576-9379
Gives you a bit more freedom in connections between cells than the the setups with 3 or more caps fixed in a bracket. If you need more space for a hold down or something you can route the tubing around the obstacle.

Fried my old batteries because they were such a hassle to check and I wasn't religious enough in keeping them filled up. Now just pull out the jug of condensed water, hook up the bulb pump, give it a few squeezes and I'm done in a couple of minutes.

[sstuller]

I've read in golf cart forums where watering systems will share hydrogen also. If the gas from one cell ignites it expands to the rest of the cells making a battery explosion much worse.

[exMaggieDrum]

Originally Posted by jwcolby54

the ideal place to do this on my boat would be all the way at the back against stern wall. There's a lot of room back there under the cockpit and the seats have hatches which lifts up, which would allow me to use ropes and pulleys to get the batteries down in there.

But 700 pounds feels like a lot of weight to put that far back on a 33 foot 14000 pound boat.

It would be far better to put 700 pounds near the mid-center line of a 33' boat. In the far stern you will have way to much weight that is unbalanced. That of course would depend on the specific characteristics of any boat but it would be surprising if it were designed to handle that type of load in that location. I would also be concerned about the effect of that much weight on the structure in that location. It would have to be well-reinforced.

[settingsun]

We've lived exclusively on solar powered batteries for over 8 years on our boat and in our RV. We've had both 12 volt (4D) and 6 volt (golf cart) and wet cell and AGM batteries in different configurations ranging from 220 to 710 amp-hours, and we've learned a lot about batteries and battery charging in the process.

We've put together some information to help our fellow cruisers figure out what battery systems will work best for them and how to keep those batteries charged, whether using the engine alternator, a converter, inverter/charger or solar power.

I hope this is useful...here's the link:

RV and Marine Batteries