What is the point.

Just a quick aside: Before accepting any batteries,check that they are full.I bought a set at Sam's club and found one was bone dry after I got home,naturaly.

The Costco Group 27 RV/Marine batteries aren't "true" deep cycle batteries, but rather are a hybrid type with starting capabilities. However, in our older Roadtrek which has room for only a type 24, we use the same kind of battery (95 Ah) with very good results. We have a small solar panel on the dash that keeps the house battery fully charged when the Roadtrek is being stored.

Regarding the Costco type 27 battery cited by Thrifty Dutch, our starting battery needed replacement, and this battery was the least expensive, and starts the Roadtrek easily in all weather conditions. As we use a 1500 W inverter connected to the engine battery to power the microwave oven, this type of battery serves us well. (We run the engine when the microwave is being used.)

Another point: Costco here in Canada unfortunately doesn't have as extensive a line of automotive/RV batteries as in the States.

Does anyone know anything about the quality of the Duracell golf cart batteries. Who makes them and how good are they.

I just had a pair of GC2 go bad on me. My fault. But after having them for 2 years, I learned that I very rarely appreciated the extra capacity. Just the way we camp. So I replaced with just one group27. Cheaper and saved about 80 pounds on my tongue.

I'm not sure I made a good choice, but I'll be finding out.

BTW, GC2's are $80 each at Costco.

Some points to make here.

Are you certain the Costco batteries are 115ah at 20 hour rate and true deep cycle. Not deep cycle/starting, not 115 reserve power, generally wouldn't ever be rated with cold cranking amps if true deep cycle. I have a Costco 12v group 27 alleged deep cycle battery/starting that was rated over 100ah (don't remember exactly). Did a capacity test on it when it had a few cycles on it and it tested closer to 85ah, which is typical for that kind of battery. After a bunch of calls, I got through to the manufacturer, and they said it was rated at the 100 hour rate. which makes the capacity much higher. Definitely cheating as everyone uses the 20 amp rating.

It is also very rare to find a high quality true deep cycle in the 12v style. Crown and Trojan make some, but almost all the others are not all that great, and even an SCS200 12v Trojan has 1/2 the cycle life of the Trojan golf cart 6v batteries.

It is also very rare to find a NON true deep cycle 6v GC2 battery, as they are all designed for golf carts. The manufacturers focus on durability and capacity for that market.

The statement about the 6v charging faster, IMO, is backwards. The 12v batteries that I have seen usually charge considerably faster than the GC2 6 volts. We had both in our Roadtrek for quite a while, all were Trojans and the difference was pretty large. The 6v will also give up the charge a bit slower, so more voltage drop at very high amp draws. For most this is not an issue, as 220ah of 6v batteries will run a 100 amp load OK down to about 50% state of charge.

Most GC2 batteries will have around double the cycle life of most the 12v ones. (there are always exceptions)

Arguing over the 12v parallel vs 6v series wiring is kind of moot. With two 12v in series, they can see different currents based on their internal variations, as they see the same voltage. With two 6v in series, they can see different voltages based on their internal variations, as they see the same current. Both have a mismatches but of different types, and both mismatches give uneven charging. That said, the 6v batteries, especially if they come from the same manufacturing run, tend to match much better than the 12v ones do. It makes sense as 12v batteries are commonly used alone, and golf cart 6v batteries are almost always used in multiples, so they have to match better.

Personally, I would never use two 12v if two 6v would fit. If Costco is carrying the Interstate GC2 6v batteries (they have switched to Interstate on everything, I think) they are likely pretty good batteries, at least the used to be. Others have had decent luck with the Walmart or Sam's club 6v batteries.

Judging by your name Thriftydutch I'd say go the cheaper route.You will need to replace the 12 volts sooner because they simply have less lead in them, but the 12 volts will be lighter and easier to move around.There is a reason most RV manufacturers go with 2 6 volts and it ain't cheaper price.

The only real difference between two 12 volt true deep cycle vs the two 6 volt true deep cycle is it's easier to get the 6 volt properly charged. The same charging current goes through both 6 volt. The slight wiring differences with two 12 volt make it very difficult to get exactly the same charge/discharge on both.
Other then that it's a toss up. We went the 12 volt route only because in a pinch I can pull one and charge it in the back of the truck while exploring the back roads.

loggenrock wrote:
The way I understand it, any flooded lead-acid battery should never be discharged less than 50% without causing damage to the cells (hence shortening the life of the battery). Given the data you provided, 50% discharge of your 12v battery yields approx 57 amp-hours. x 2 is 114 ah total usable capacity. The 6 volt batteries at 50% give 116 ah EACH, so you should have approx twice the usable amp-hours if you were to change to the (2) 6v, which are true deep-cycle ones. The 12v are likely trolling-motor style, meaning they are capable of providing high amperage discharge rates to start things, not just a steady discharge like a true deep cycle. All the other comments on 12v vs 6v are accurate, meaning one dead 6v battery leaves you out of service, etc. But unless you do a lot of extended boondocking without either running the engine driving about, a generator running, or solar panels, then having the extra battery storage capacity is rather meaningless. Hope this helps!



ST

Actually that's not how it works as far as amp hours. That 6V's and has to be doubled to 12V, so the two banks he is comparing are really just about equal as far as amp hours. Otherwise you are dead on.

The way I understand it, any flooded lead-acid battery should never be discharged less than 50% without causing damage to the cells (hence shortening the life of the battery). Given the data you provided, 50% discharge of your 12v battery yields approx 57 amp-hours. x 2 is 114 ah total usable capacity. The 6 volt batteries at 50% give 116 ah EACH, so you should have approx twice the usable amp-hours if you were to change to the (2) 6v, which are true deep-cycle ones. The 12v are likely trolling-motor style, meaning they are capable of providing high amperage discharge rates to start things, not just a steady discharge like a true deep cycle. All the other comments on 12v vs 6v are accurate, meaning one dead 6v battery leaves you out of service, etc. But unless you do a lot of extended boondocking without either running the engine driving about, a generator running, or solar panels, then having the extra battery storage capacity is rather meaningless. Hope this helps! ST