12V or 6V Batteries - Which charge Better?

Along with considering AGM batteries, you might want to invest in an adequate solar panel array to do the charging and give your generator a rest. I have two 6V AGM batteries in series along with 200 Watts of solar panels. Before this set up, I'd have to run my genset for 3-4 hours a day. Now, I only fire it up if I'm using an appliance that needs 120 volts such as the microwave.

Yes, they always say that AGMs will take a charge a lot faster than flooded batteries.

I went with Trojan Group 27 AGM in my motor home for similar reasons. I have PD 4645 multistage converter. I have found that the battery charges fairly quickly using the genny. Not sure, I am no battery expert, but I believe AGM's are more efficient. I can tell you, though it was expensive, the battery is a brute when it comes service.

Ron,

Your question is good, and if you have read the thread through, you may feel more confused than answered. I did a lot of boat work before the depression and I got asked variants of this question by almost every owner to whom I wrote a quote. Let me try to give you a complete answer.

Lets start with the first fact: Lead acid (l/a)batteries do not play well in parallel. To answer why in detail will take another half of an hour. Trust me on this one. Avoid paralleling batteries.

Another issue of semantics that we have to clear. Recharging any l/a bank to true full density without damaging either the bank or the connected hardware will take hours. From a 50% discharge, the majority of the bulk charge can be done in about four hours with the right system, but that will end at the 85~90% area and the last 10~15% will take at least another four and maybe more hours.

You have to realize the that entire existence of an L/A battery is between 12.0 (~50%) and 12.6 (~100%) when it is in use. Its charging home is between 13.5 and 14.4. Less takes forever and more starts to hurt things.

The only thing that can improve the charging rate is to go to a variety of l/a battery called an AGM. Price these and you may just stop there. They are good, but you pay for it up front.

If you had a pair of 12V in parallel and a pair of 6V in series of roughly the same Ampere-Hour capacity, and both banks were drained the same amount, Recharging them to the original density would take the same time with the same hardware. That is all there is to that. Except, as they age the two 12V will get cantankerous and you may have a hard time getting both to density at the same time. See the second paragraph.

So, If you want to have a house bank that lasts well and you can recover it relatively quickly with your APU (genset), a very simple recommendation will be: a pair of GC2 batteries in series,
A good three or four stage "smart" converter charger (Progressive Dynamics or Iota or ??), The converter mounted as close to the bank as practical and connected with short Heavy Cable.

Why???
GC2s are golf cart batteries and they are real deep cycle. Most 12v that are sold as Marine Deep Cycle are not. They will not stand the abuse that a GC2 will take in stride.
A good smart converter/charger will sense that the bank is low and go into bulk mode as soon as it has power. It will, however, not exceed the mid-14s as higher than that has a tendency to toast the DC powered stuff and heat the batteries (not good).
The short heavy cables are essential. The charger only knows what it can't exceed and if you burn off even a tenth of a volt on the way to the bank, your required charge time will be extended.

That is most of what you or anybody else needs to know and think about. If you want to know what is really happening, get and install a real battery monitor system. (~250$us for hardware) These have names like Trimetric, Victronic and Xantrex and will report the real bank status based on the ampere-hours taken out and replaced. If you put one in, be ready to learn a lot fast.

Matt

If both options have the same amp-hour capacity and assuming both are equally discharged, the difference in charge time should be insignificant. Running your engine should charge them much faster than your genny powered converter unless you've installed a converter with incredible output amperage. Don't forget that for best battery longevity, you don't want to discharge the battery bank beyond 50% of its amp-hour capacity. A Trimetric Battery Monitor is a good way to keep track of your battery charge or discharge. It's pretty hard to guess when the batteries are fully charged up without some kind of instrumentation.

Charging speed will depend more on the converter and battery connection than battery voltage.
Generally the 2x GC2 has a bit more capacity so good chance they will take a bit longer but not much.

I believe RoyB addressed this issue rather well, but my question is what do you mean by "drained" ? Trojan web site indicates that GC batteries can be taken to 20% but will lessen the life span of the batteries. No more than 50% is recommended for longevity.

As far as using the generator and its on board charging system. My answer is also no,
I use a portable Smart charger connected to the Genny, directly to the batts.

My on board converter in my TT is absolutely worthless for any charging.

Ron, if you are using your built in converter-charger, and if it is a Parallax or WFCO, your question unfortunately is moot. The batteries won't be the limiting factor. IMO, if you have the height for the 6v batteries, go that way. They are designed for deep cycling. Normal 12v Group 24 and 27 batteries say deep cycle on them, but they are a compromise between deep cycle and starting.

Menards carries an Exide Nautilus Marine Deep Cycle 12v Group 27 which, according to the Exide website, is NOT a compromise deep cycle/ starting battery, but rather a true deep cycle. I have not tried it but if I was going Group 27, I would try that.

Your comment of charging with your generator is only valid if you connect your trailer shore power cable to the generator 120VAC receptacle using a proper ADAPTER which will allow your on-borad smart mode conevrter/charger unit to re-charge your batteries.

If you are refering to the BATT output connector on some generaters you will find they only produce some unregulated DC OUTPUT voltage around 12VDC with the capacity of maybe 6-9AMPS. This connector will take a very long time to charge a deep cycle battery. You need to start with 14.4VDC with the DC CURRENT Capacity of 17-20AMPS of DC CURRENT for each of your connected batteries. This is only developed from the trailer on-board smart mode converter/charger unit or an external portable smart mode charger unit you may have plugged into the generator.

Roy Ken

The time a deep cycle battery takes to re-charge depends on the DC Charging voltage and how much DC Current it can pull from your charger.

A 12VDC Deep Cycle battery will usually get to its 90% charge state in a short three hour time if you present 14.4VDC Charging voltage with the capacity of 17-20AMPS DC CURRENT per battery being charged..

Consider what PROGRESSIVE DYNAMICS says in just about all of their converter/charger manuals on how long it takes a typical deep cycle battery to re-charge.

"Progressive Dynamics ran this test on the amount of time it took a PD9155 (55-amp) converter/charger set to three different output voltages to recharge a 125 AH (Amp Hour) battery after it was fully discharged to 10.5-volts. 14.4-VOLTS (Boost Mode) –

Returned the battery to 90% of full charge in approximately 3-hours. The battery reached full charge in approximately 11 hours.

13.6-VOLTS (Normal Mode) – Required 40-hours to return the battery to 90% of full charge and 78-hours to reach full charge.

13.2-VOLTS (Storage Mode) – Required 60-hours to return the battery to 90% of full charge and 100-hours to reach full charge."

This is battery charging science at play here. You can charge your battery quicker by raising the 14.4VDC to a higher DC VOLTAGE and the battery will then demand more charging current. The downside to doing this is you will start boiling out the battery fluids if you are charging with more than approximately 14.4VDC at a higher DC CURRENT demand.

I can re-charge my 12VDC batteries back up to their 90% charge state in about three hours charging time and can expect almost full performance capacity out of my battery. I can do this 50% to 90% charge cycle for 12-14 times where I must do a full 100% charge state. Continuing to re-charge only up to the 90% charge state without doing a full 100% charge cycle will do harm to your batteries.

In your case of using two two 6VDC batteries in series you would charge the two of them at the same using the 14.4VDC charging voltage. This would be considered one 12VDC battery.

Some batteries will deviate a tad from the 14.4VDC depending on how they were made. Trojan likes to have a higher charging DC Voltage...

This is all based on my experiences - no expert here by any means...
Roy Ken