Adding new batteries to an existing bank

cfcw

Hey guys, I have a small experimental system- 2 GC batteries for 12 v ~220 Ah. I'd like to add some battery capacity to my setup. I have read this is a real no-no but they are only about a year old. They have floated pretty much their entire life since purchase, I've only cycled them to 50% SOC maybe ten times. So, can I add to this bank with new batteries without concern? What say the experts? Thanks!

Cariboocoot

Re: Adding new batteries to an existing bank

Experts? Where are we going to find them?

Experimental system, kept charged, not cycled much, good SG readings, less than 1 year old ... no worries.

n3qik

Re: Adding new batteries to an existing bank

2X on that. My current system has two that are a year older than the rest. They where used on a UPS system I had.

Photowhit

Re: Adding new batteries to an existing bank

I'm on the other side of the fence on this, I'd say abuse what you have and start new in a year or 2.

Particularly if your not adding solar panels to your 128 watt array. or changing to a 24 volt inverter or something requiring the change.

Then again you could find you can't kill those stinking batteries (I was in the same spot when changing from a 220 watt array to a 1000watt array, though I had switched to 4 GC batts a little over a year before knowing I would at some point, Thats now 4 years ago and they are really hanging in there...)

I have added a 6 volt battery to a battery bank (2 batteries about a 300 watt array before I broke a 90 watt panel) less than a year old, it was replaced under warranty, but I always had problems after that (the voltage at rest dropped to 12.4 after about 12 hours off array and later after charging off AC, I wasn't sophisticated enough to check the SG at the time, no load just a cheap car inverter attached, I recall checking the batteries against each other and they were close, but only after they had fallen, not before this is about 15 years back.) and gave up and replace both within a year.

icarus

Re: Adding new batteries to an existing bank

Ok, I'll chime in, right down the middle. If you need more capacity, feel free to add capacity as 'Coot suggests. There is little down side.

On the other hand, as Photowatt suggest, if you are just messing around, and experimenting, kill the starter set, and then start fresh after you have figured out how to kill (and not kill) them.

Tony

Cariboocoot

Re: Adding new batteries to an existing bank

We need to clarify: if you add more battery capacity you need to add more charging capacity as well.
Not sure how many 128 Watt panels the OP has, but two would be about at their limit for 220 Amp/hrs.

Kamala

Re: Adding new batteries to an existing bank

Would it make a difference if these were FLAs, GelCells or AGMs?

Seems like it should. And this distinction is often ignored. Often, in this forum, FLA seems to be assumed.

Cariboocoot

Re: Adding new batteries to an existing bank

Kamala wrote: »

Would it make a difference if these were FLAs, GelCells or AGMs?

Seems like it should. And this distinction is often ignored. Often, in this forum, FLA seems to be assumed.

Actually the "2 GC batteries" in the OP's post probably indicates Gel Cell.
The advice is generic and applies to all: young batteries, kept up, not deeply discharged, experimental system - it shouldn't be a major concern.
But there are some people who think a few months difference in manufacture date can be a problem.
You could say it's a question of how much performance difference is acceptable to you and your particular application (as in the eternal mixing dissimilar panels debate).

Just my opinion, as usual, and everyone is free to disagree with it, as usual.
As long as it's not my nickel being spent, it doesn't matter to me.

Kamala

Re: Adding new batteries to an existing bank

Cariboocoot wrote: »

Actually the "2 GC batteries" in the OP's post probably indicates Gel Cell. ...

I thought likewise. But on second thought it seemed more likely GC meant Golf Cart. I've used that abbreviation myself.

K

Cariboocoot

Re: Adding new batteries to an existing bank

What we shouldn't gloss over is that the new batteries must be the same as the old ones!
Same make, model, size, capacity.

You can't mix different types (like AGM with FLA) or capacities (225 Amp/hr with 390 Amp/hr).
Even the same batteries will have some performance differences, but should be close enough that it won't cause problems. The older the batteries are or the more used/abused the less success you'll have with adding new ones.

Kamala

Re: Adding new batteries to an existing bank

Cariboocoot wrote: »

,,, You can't mix different types (like AGM with FLA) or capacities (225 Amp/hr with 390 Amp/hr). ..

Agreed, with enthusiasm! But what is the morphology of the battery in question?

One morphology might be more tolerant of such age mismatches than another. Maybe not. I'm wondering.

K

niel

Re: Adding new batteries to an existing bank

Kamala wrote: »

Agreed, with enthusiasm! But what is the morphology of the battery in question?

One morphology might be more tolerant of such age mismatches than another. Maybe not. I'm wondering.

K

if you are referring to the different types of batteries then imo i would not do this for gelled batteries 1 year apart as gels are more picky. the other types would most likely be fine to add more capacity to as long as the op can deliver a proper charge to them all and as coot said they must be an identical battery to the originals.
my take is he is referencing to golf cart batteries as 220ah is common for them even though it is possible to have a 220ah gelled battery.

cfcw

Re: Adding new batteries to an existing bank

Hey Guys, sorry for the delayed reply. I have been out of town and away from the computer for a few days.

Thanks for the input and sorry for the confusion -The GC is "golfcart" two 6V lead acid golf cart batteries bought at Sams last year. I do have only about 9.5 amps of solar capability but on these batteries I have my prosine 2.0 hooked up to it, so charging rate shouldn't be an issue. I know that 240Ah of batteries is probably less than I should have on the prosine if I was to pull rated loads. I hope to increase my PV charging capability but my lot is very shady. I currently have two 64 unisolar panels that I have made into a portable setup, but I usually hook those up to a 140 AH AGM battery I also have.

BTW, what is max suggested draw rate on lead acid?

Cariboocoot

Re: Adding new batteries to an existing bank

cfcw wrote: »

BTW, what is max suggested draw rate on lead acid?

There isn't one, per se. You can have quite massive FLA banks and churn out huge amounts of power. It's a matter of how comfortable are you with increasing current and/or Voltage.

As for any given battery, it's all according to the manufacturer's specifications.

BB.

Re: Adding new batteries to an existing bank

Regarding recommended loads for flooded cell batteries... The recommended rule of thumb:

• C/20 for long term average (efficient discharging/charging)
• C/10 for higher loads/smaller bank (less efficient discharge)
• C/8 for long term maximum draw (batteries can overheat if higher continuous current draw--monitor temperature)
• C/2.5 for surge current (higher currents can depress output voltage and cause issues for load or cause high battery voltage if charging current).

For some AGM battery brands/models, they can even support C*4 charge/discharge rates--but that is a heck of a lot of current and be very difficult to connect cables heavy enough for those levels of current.

-Bill