# 6 Volt vs 12 Volt Batteries

Solar Expert Posts: 52 ✭✭✭✭
Some guides I'm reading state that 6 volt batteries are better than 12 volt batteries with solar powered systems. In particular one guide described 6 volt batteries as "truly deep cycle batteries". A golf cart was used as example where the batteries are drained almost completely daily after hours of usage and charged again nightly.

Would it be true to say that I can safely drain more power out of a 6V battery bank setup than a 12v battery bank setup?

• Solar Expert Posts: 292 ✭✭✭✭✭✭
Re: 6 Volt vs 12 Volt Batteries

Different batteries have different parameters for charging and discharging, but for long term use you need to keep from taking them down below 50%. The less discharge the longer the life. Only taking them down 20% is better than 50.
Others will give more detailed answers.

Edit
You probably won't find much that runs on just 6v. Six volt batteries are put in series to get multiples of 12. 12, 24,48
• Solar Expert Posts: 225 ✭✭
Re: 6 Volt vs 12 Volt Batteries

I will be interested in other replies. What I see is a great number of "opinions" and a great deal of myth and magic. If the internals of the 12 or 6V are the same there will be no advantage, therefore it is the quality and type, AGM, wet... that makes the difference, or no difference
• Super Moderators Posts: 26,666 admin
Re: 6 Volt vs 12 Volt Batteries

There are certainly differences between Auto, Deep Cycle, and even ForkLift batteries (not including AGM, GEL, VRLA, etc.)...

For me, I first like to see what the voltage and AH capacity of the bank will be--then start looking at batteries (and their costs) to fit the need.

My suggestion, is to try and keep to a single series string of cells.

If that is a small 100 AH 12 volt bank--Then feel free to use a single 12 volt 100 AH battery.

If it is a 220 AH bank, then use several 6 volt @ 220 AH deep cycle (aka Golf Cart Batteries) to make your single string bank.

As the bank AH capacity increases, you have a choice a a bunch of smaller AH cells in series parallel (like a bunch of 12 volt or 6 volt cells), or now-a-days, some folks are making high AH rated 4 volt and 2 volt cells that you can put in series to make a single battery/cell string (or 2-3 string--my recommended maximum parallel unless you no other option).

Note, if you have lots of parallel strings, you will have more cells to check/water. There will be more chance of one or more failing cells that can damage a string/bank (open/shorted cells) that you may miss, more connections to monitor/clean.

And, when you put more than two strings together in parallel, each string should be protected by a high amperage fuse or circuit breaker (more money--big battery banks can output 1,000's to 10,000's of amperes into a dead short--be careful).

One thing that makes keeping track of parallel battery strings easier is to monitor each string's current during heavy charging and discharging... You will quickly find any string that is not at "average" performance (looking for open/shorted cells, dirty connections, etc.). These days, even a \$60 DC Current Clamp Meter is "good enough" for this basic inspection/debugging of your battery bank (and the rest of your solar PV system).

One of the questions that will have to be asked/answered is your access to where the batteries will be stored. If you have to hand carry them down stairs into a cellar--You probably don't want much over 200 lbs each (for two people to carry).

If you have a flat concrete area with access to a pallet jack/forklift/crane--then you can even look at some 1,000-2,000 lb Fork Lift Batteries (12/24/etc. volt).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Banned Posts: 17,615 ✭✭
Re: 6 Volt vs 12 Volt Batteries

The Voltage doesn't make any difference. Only the battery type.
The reason people pick 6 Volt batteries is because the golf cart batteries are a really inexpensive way to get some serious deep cycle Amp hours at a bargain price.
• Solar Expert Posts: 52 ✭✭✭✭
Re: 6 Volt vs 12 Volt Batteries
The reason people pick 6 Volt batteries is because the golf cart batteries are a really inexpensive way to get some serious deep cycle Amp hours at a bargain price.

For a second there I got excited... but then I remembered I need two 6v batteries to make a 12v systems. In this case the 12v battery is probally a more cost effective solution.
• Solar Expert Posts: 3,009 ✭✭✭✭
Re: 6 Volt vs 12 Volt Batteries

Unless something better comes along, my next bank will be six of the 2 volt, L16 size in series, instead of the six, 6 volt L16's I now have. No more series/parallel strings and multiple connections like I have now. And only 6 cells to check and water, instead of the present 18 !
• Solar Expert Posts: 69 ✭✭✭✭
2 Volt

Here is a positive vote for the 2 volt cells.
I have a nice series string of Twelve Rolls S-1590 2Volt, 1200 AmpHr flooded lead-acid cells. they are only 121 pounds each, so easy enough to move around, and only one cap in the center to check/ fill electrolyte.
20 hour rate is 1200 AmpHr
72 Hour rate is 1512 AmpHr
Full battery specs here:
http://www.rollsbattery.com/pdf/S-1590.pdf
• Banned Posts: 17,615 ✭✭
Re: 6 Volt vs 12 Volt Batteries

Yes, if you need the massive Amp hours 2 Volt is the way to go. It eliminates the perils of parallel pairing.

Big Amp hours still need big Amps to recharge, no matter how you divide them up. That's why I prefer limiting the Amp hour capacity of a bank to something that can be handled by a single charge controller, and increasing the system Voltage if more Watt hours are need. Of course once you hit 48 VDC you've no choice but to expand the Amp hours.

Let's see ... 1000 Amp hours @ 48 Volts ... roughly 24kW hours. Or ten times what I use. And that brings us back to conservation, conservation, conservation.