Adding a second battery to existing battery

[psytechguy]

I currently have a 108 AH SunExtender AGM (Concorde?)
It's been online for about 2 years and has never been discharged below 80% capacity. Always charged to 100% by noon the next day.

I've heard over and over again that you should always pair batteries of the same age and never add a brand new battery to an older battery bank, but I'm wondering if I can get away with adding another SunExtender to double my capacity without compromising the longevity of either battery too badly. I'm planning on adding a few things in the near future that would increase my power consumption, i.e. ham radio, computer, etc.

I really hate the idea of having to spring for 2 brand new batteries just to double capacity when this battery seems so healthy.
... but I'd also really hate to screw up an expensive battery!

At my current daily discharge/charge rate, this battery is rated for ~3000 cycles, so it's been through about 700 or so.

I'm running 460 watts of panels through a 45 amp Tristar MPPT controller.

Thanks!

Mike

 

[jimindenver]

Pair yours with a new battery will not be idea but not the end of the world either. Condition the older battery as much as possible to get it as close to the levels of the new and you will get wwhat you get.

 

[29chico]

I would for sure say go ahead and pair a second battery to your existing one if, and this is a huge IF, your definition of every one of those 100% charges actually matched the Sun Xtender manual charging parameters. 

Manual PDF:

http://www.sunxtender.com/pdfs/Sun_Xtender_Battery_Technical_Manual.pdf

Page 19 for the charging info.

Otherwise, just use up your existing battery.   If you charge that battery correctly, and take it no lower than a 60% state of charge when you start using more power you will still get plenty of life out of it.

 

[SternWake]

Sunextenders are the same as lifeline, but sun extender measures capacity differently.



Paralleling a new one to old is not ideal, nor will it 'double' capacity as even after 2 years of light discharges the battery has degraded to some degree.

A lot of the 'Un-ideal ' about paralleling new with old is  the resting fully charged voltage, but in a system in constant use, well there is little rest.

These lifelines also hold onto their surface charges for so long it is hard to really know when their surface voltage has stabilized.  The Brand New lifeline gpl-31xt I had for a few weeks for a friend would maintained 13.16v for 5 days, even removing 5Ah from it

One thing you could do, rather than hooking old to new in parallel permanently, is add an A-B/both/off switch so you can keep the batteries separate when discharging/ resting, and combine them when charging, or when running heavier loads.

How much benefit to the batteries by being put on a switch, really depends on how much the older battery has degraded in 2 years of light cycling, and much of that is dependent on how well your solar controller actually meets the definition of a full charge.  Those controllers that cannot be programmed  as to absorption voltage or its duration, do poorly.  A good solar controller pays for itself in battery life, as long as the user programs the ABSV duration correctly for their use.

Determining full charge on lifelines is pretty easy.  When amps taper to 0.5% of capacity( use the 20 hour rate given on the lifeline model that correlates to the sunextender) at absorption voltage, then the battery is full.

A solar controller reverting to float voltage is often taken as a sign the battery is full, but this does not mean that at all.  It takes quite a long time for amps to taper to 0.5% of capacity at absorption voltage.  No less than 3 hours from 80% charged.  This time to full is the silent lead acid battery killer.  It simply takes so long and achieving full is so important for getting anywhere near the manufacturer claimed cycle life, which is established with absolute perfect recharges, in a lab, each discharge cycle, promptly.

So if your charge controller, for 2 years, only got the lifeline back to ~98%, it has degraded/lost more capacity than you suspect, and a new battery put in parallel with it will degrade much faster as it has less resistance.  It will do much more of the work and constantly be trying to raise the voltage of the older battery.

Having 2 batteries in parallel reduces the Peukert effect, compared to cycling one battery, then the other, but if the loads are less than ~ 5 amps then this is negligible.

 

[akrvbob]

Since you have surplus solar and too little battery, an option is to run the cable from the controller to an A-B switch and then from it to each separate banks of batteries. After the old battery is 100%, switch to the newer battery. Just be careful with them so that you don't take the new battery down too much and always gets up to 100% daily or every other day.
Bob

 

[psytechguy]

Lot's of good info and ideas here guys! I appreciate it!

I think I'm going to go ahead and add the computer and radios to the mix first and just see what happens. If I start pulling it down to 60% or lower and can't get 100% charge daily, then I'll decide on battery options.

The main reason I suppose I'm all fired up to make changes right now is that I'm currently in the Flagstaff area and the solar store is there.

 

[rvpopeye]

When I first started reading this thread .
I was thinking , two unmatched batteries would fight to be at same voltage.
The new one would lose to the old one .
Then I thought A/B switch to separate them.
Then I started to read the rest of the posts and then I was thinking "what Stern and Bob said", add my vote !
Your idea to go with what you have now and see how it works out seems to be the best approach for economy and , hey, you'll probably be pleasantly surprised .
If not ,THEN think about something different as above.......

 

[29chico]

SternWake:

Before I put up the above #3 post yesterday I knew that I was not sure about the differences between Concorde's Sun Xtender and Lifeline product lines.  So I called and had a great conversation about just that with a tech at Concorde.  He said that the Sun Xtender line is engineered to be a better off grid solar battery and better withstand deeper discharges and to be more tolerant of the lower amps of recharging current that is often the case with stand alone solar systems. Also, the main difference between the two product lines is in the formulation of the lead paste that is applied to the plates.

We also discussed the lack of cranking amps in the specs on the SX line vs the cranking amps being included in the specs for the Lifeline batteries.  My take on that part of the discussion is that Lifeline's are Concorde's version of a hybrid marine starting/deep cycle application while the SX's are intended for true deep cycle use & abuse.

FWIW, the tech also said that the Lifeline's an SX's are both equally resistant to the vibrations that result from mobile use.

 

[SternWake]

SternWake:

Before I put up the above #3 post yesterday I knew that I was not sure about the differences between Concorde's Sun Xtender and Lifeline product lines.  So I called and had a great conversation about just that with a tech at Concorde.  He said that the Sun Xtender line is engineered to be a better off grid solar battery and better withstand deeper discharges and to be more tolerant of the lower amps of recharging current that is often the case with stand alone solar systems. Also, the main difference between the two product lines is in the formulation of the lead paste that is applied to the plates.

We also discussed the lack of cranking amps in the specs on the SX line vs the cranking amps being included in the specs for the Lifeline batteries.  My take on that part of the discussion is that Lifeline's are Concorde's version of a hybrid marine starting/deep cycle application while the SX's are intended for true deep cycle use & abuse.

FWIW, the tech also said that the Lifeline's an SX's are both equally resistant to the vibrations that result from mobile use.

Call me skeptical, but I am not buying it.  If true would make for such a better battery as to make the lifeline obsolete.

If true there would have to be a downside to the sunEX lineup, some trade off, as their price is about the same as Lifeline.  if the paste material were different and somehow was just fine and dandy with low and slow recharge rates in deep cycle applications, it would lose some other attribute, such as super low self discharge or the ability to accept huge charge rates without gassing.

The PDF you linked to and the one for lifeline are nearly exactly the same, both say that a minimum current of 20% be applied when cycle to 50% or below., and that the higher the charge current the better.  the 'conditioning' and deep discharge recovery procedures are the same.


I am a cynic but I believe they just slapped a new sticker on the lifeline, and the tech you spoke with was an 'applications engineer', a marketer with an accounting degree, trained by lawyers, and if they follow this forum, perhaps will set someone to rewriting the sunextender tech manual so that it is not exactly the same as the lifeline.

I know I once made a similar doubt about the trojan t105 and the t-105re but then was informed the RE was taller and heavier.  I once Emailed trojan about the difference between the t-1275 and the J150re and the guy told me they were the same exact battery with different handles  Their spec sheets have the j150re as 2 Lbs heavier.  He did not address my questions about the wide range of 'acceptable' absorption voltages listed on the RE lineup, and I let him know my disappointment in the lack of reply on that topic, their spec sheets having different weights indicated, and the reply to that was just his phone number, as if he did not want to put anything in writing.

I never called.

Without any evidence one way or the other, I think the sunextender line is just Concorde marketing their Lifeline battery for the renewable markets, and why would they not?

The renewables market is ripe for the pickings, and lead acid day's as a electrical storage medium are numbered, so they have to cash in.

Thankfully Concorde batteries are likely as good as a deep cycle AGM can get, and they have not offshored production, so i can forgive them their marketing ploys to cash in on the renewables market.

But I could be wrong, and just a cynical insufferable douchenozzle, and a hypocrite .

 

[akrvbob]

Lot's of good info and ideas here guys! I appreciate it!

I think I'm going to go ahead and add the computer and radios to the mix first and just see what happens. If I start pulling it down to 60% or lower and can't get 100% charge daily, then I'll decide on battery options.

The main reason I suppose I'm all fired up to make changes right now is that I'm currently in the Flagstaff area and the solar store is there.

I'm pretty close by, just south of Ash Fork on 89. I'm moving to Williams which is 30 miles west of Flagstaff very soon. Be great to meet you!
Bob

 

[jimindenver]

It's no different than antennas being sold as HD or wilson repackaging the Sleek as the WeBoost. No difference but you have to provide what people are looking for even if you have had it all along.