Should I use Trojan or Interstate batteries?

10 Posts
Jan 13, 2009 04:02 pm
Should I use Trojan or Interstate batteries?

I'm torn between price and distance to travel. Interstate dealer is approx. 30 miles away, about a 1 hour trip, and Trojan dealer is less than 2 miles away, about a 5 minute trip. In the L16 size the Interstates are about $40 cheaper.
Are the Trojans worth the extra money?
I have an Outback system, 48 volt, VFX3648 inverter, MX60 charge controller, 1340 watts worth of panels. My plan is to add another 680 watts of panels this summer to get up to 2020 watts. And it's Not a grid-tie system. Just to get the system up and running I hooked up (4) 12 volt Marine/RV batteries that were lent to me, they are useless and need to be replaced asap, they severly limit the system right now.
So another question, with my realatively small amount of solar should I go with a smaller battery? say like a T145?
I have no real goals as far as production, I just use whatever I can make, when the solar isn't there it just switches back to the grid. Basically the solar suppliments my electric use.
Any advice would be appreciated, Thank you.
351 Posts
Jan 14, 2009 05:41 pm
Re: Should I use Trojan or Interstate batteries?

I am far more concerned with the size of your battery bank, than who makes it. You did not specifically mention size, but I get the impression you are talking about eight batteries.  You should not go smaller. I think you should be going larger, if you want a long life for your battery bank. How much larger depends on where it is located.

Your comment that you just use whatever you make, is bothersome.  How deep of a daily discharge are you planning for this new bank?

10 Posts
Jan 15, 2009 08:55 am
Re: Should I use Trojan or Interstate batteries?

Well its a 48 volt system, and L16's are 6 volt, so yes that would require 8 batteries.

I guess the main point of my question were:
1) Are the Trojan batteries worth the extra cost? Rechecking its $55 a piece extra. Will they last longer, be more reliable, will I get more cycles than I would with the Interstate batteries?
2) Will my 1300 (eventually to be 2000 watt) array be enough to maintain L16's? or should I use a smaller battery like a T145? Keep in mind I'm located in Central NY, a good day for me this time of year is 2Kwh, and zero production days aren't uncommon.

System setup is handled. I only have select non-essential loads tied to the outback power panel. I'm not trying to get off the grid, the solar just supplements my electric supply. Between the solar and conservation I have cut my grid dependence in half, imagine if everyone could do or did that...
Right now I have the inverter set to run solar until the batteries fall to 50% when it will then seamlessly switch the loads to the grid, once the batteries reach at least 75% then it automatically toggles back to the batteries. And note that I do not charge the batteries from the grid, the loads just switch to grid power and stay there until the solar brings the batteries back up.
Once I get new proper batteries I will probley bump up the set points to a shallower depth of discharge so to take it extra easy on the batteries and get as long a life span as I can from them.

So if anyone has any opinion or data on Trojan vs. Interstate bang for the buck it would be appreciated.
Thank you.
220 Posts
Jan 15, 2009 12:52 pm
Re: Should I use Trojan or Interstate batteries?

 hi gordon,

 sometimes finding battery data for different brand names can be a daunting task. it could carry a name like "interstate" or "big bobs battery" or whatever name. one of the ways to find the actual manufacturer of the battery is to have a look at the MSDS (material safety data sheet) that is required to be available for all batteries sold in the us. when we pull the interstate sheet we find it's made by the u.s. battery corporation.

 here is a homepower battery chart of the big players in the battery business. i uploaded this info off site using member privileges* from homepower magazine.

 here is some cross reference info about who makes what under what name.

  i have heard some interesting stories from workers in the battery trade that many times the same "core" is labeled with different specs based only on the warranty provided with the purchase.

  it's your hard earned cash and wanting the best bang for your buck is worth the extra reading time.

 some more good info here.

 and here. with more links for drilling.

 *finally a plug for homepower magazine  week after week and month after month the folks on this forum have repeated the advice about getting a homepower subscription and i finally caved when the price dropped to it's current price ($65) for the whole shebang. thats all web based services as well as the full publication database on cd from it's conception, over twenty years worth!

 hope this helps, dave
10 Posts
Jan 15, 2009 01:25 pm
Re: Should I use Trojan or Interstate batteries?

Yep, I've got my homepower subscription, recent loyal subscriber. I was looking at the battery buyers guide in the Oct/Nov 2008 issue, and it failed to mention Interstate, but I do see now that it lists US Battery. On the surface it looks like the Interstate / US Battery has better specs as far as number of cycles.
But once I get home tonight I'll be sure to pour over the host of info you supplied.
Thank you so much.
351 Posts
Jan 15, 2009 02:47 pm
Re: Should I use Trojan or Interstate batteries?

Here is an article for you on the life and death of batteries.
Take a look at the section and chart about halfway down, on depth of discharge.

While you may only be getting two hours of full sun now, this summer you should be getting something around 4.5 hours. With your current panels, it is about 6KWh or 125Ah a day. When you increase the panels, it will be closer to 9KWh or 189Ah a day. 

189Ah would equate to a 50% DOD on the 37AH bank of eight batteries. 
I would give serious consideration to increasing your bank size to 16, and limiting the depth of discharge to about 25%.  If you cut your daily draw in the winter to something close to your generation, you would be running less than 10% DOD during winter.  That should more than double the life of your batteries. (Talking about the life of the L-16’s, not your previous batteries)

As far as which battery to purchase, I have had good service with both.  Interstate makes a good battery, but I believe the Trojans are a little better, and give a longer life in identical service. 

I glanced at the info Dave supplied, and question the 3300 cycle life for “Interstates” vs 2800 for the Trojans.  We cannot safely assume that the US battery L-16 listed and the Interstate L-16 are identical. I would also look at the warrantee. USB 1 year, Trojan 7 years (I believe that is 3 years free, and prorated to 7).   

 If it were me, I would go talk to the Trojan dealer and see what type of deal he would be willing to make for me on a bank of 16 batteries.  If you are going with eight, you might as well go with the Interstate and put the “saved” 55 dollars towards your next battery purchase.

10 Posts
Jan 15, 2009 04:02 pm
Re: Should I use Trojan or Interstate batteries?

Thanks for some more good info.

The Trojan dealer I spoke with also carried US Battery, but they didn't have eight in L16 or a golf car size, and since they had to buy them by the truck load they didn't know when they would have at least 8. Plus they claimed the Trojan's were a much better battery. But who knows, that could just be them steering me towards what they had.

At this point I'm leaning towards the Trojan's, partly for the convenience of a local dealer, vs. having to borrow a truck and blowing half a day going to get the Interstates.
But I don't want to go with 16 batteries, one, I only built a battery box big enough for 8, and two, that would be quite a change to come up with.

I got the system on-line mid September, and at that time I only had 1000 watts worth of panels. Even then I was pulling close to 4KWh a day, and that was with a small shading issue, a pine tree that will be removed soon.

Thanks again for all the info.
220 Posts
Jan 16, 2009 05:28 am
Re: Should I use Trojan or Interstate batteries?


 in the last post you touched on a topic that has been bugging me for a while now. that is..does taking power off the bank as we are generating it actually count in the dod calculations or count as cycling at all? there has to be some losses but when used as made it never really goes into the battery for chemical conversion. when used like this it seems the bank should act more like a buffer than a storage battery? even more, if it were possible to have real tight control over loads it seems that very high efficiencies might even be possible.

 then again thats what the grid tie systems do without the need for the super tight load control requirements.

 i agree on the possibility of those interstate/us battery specs not being directly cross referenceable (is that a word) it's good to know where they came from thou. what is really needed is a "national clearing house" of all battery information in one place laid out on the same grid style chart for reference. now that would be a project!

 best regards, dave

 edit: gordon, we found the real interstate chart
« Last Edit: Jan 16, 2009 05:58 pm by david ames »
351 Posts
Jan 17, 2009 02:28 am
Re: Should I use Trojan or Interstate batteries?


Your question is a good one.
I think that before going into it, I want to say that the numbers we calculate are only as good as the data we have to start with.  We are making estimates, and looking for ballpark answers.  While we might come up with 21% DOD, that answer is often more precise than the data we started with. We often find that the actual depth of discharge does not match the original calculations.  We just hope the real numbers come within a few percent of the estimate.  If it isn’t, the problem will generally be in the load estimates that we are given.

Having said that:
If somehow your load matched the generation perfectly, The battery would not be in use as long as that condition was maintained. The impact of that would result in a DOD that is less than calculated. E.g.  we calc’ed for 20%, but you used 5% worth as it was generated, so the actual DOD would be 15%.  But that almost never happens.

The battery is usually charging or discharging.  If our system is generating exactly 800W, what are the odds of having exactly 800W worth of load during the day?  Usually, we will be under that figure, so the battery is charging, in spite of some of the 800W being used. If we go over the 800W (perhaps using the stove for lunch) we will experience a short minor discharge cycle in the middle of what is normally a “charging period”.  My experience is that the minor discharge cycle either doesn’t count, or you could say that it is somehow averaged into the numbers.  The figure that is going to count the most, is the greatest depth of discharge that occurred during the 24 hour period, or since the last major charge cycle.

And here, we are really talking average depth of discharge over many days.  If you run 30 days at a 20% DOD, and then have one to 50%. What does that work out to ?  20.96774% average depth of discharge over 31 days.  (How is that for an overly precise number ?) The bottom line is that you averaged somewhere in the ballpark of 21% over the 31 day period.  (And the 20 percent figure for the first 30 days was also probably bouncing around in say the 18-22% range).

A couple of percentage points really doesn’t matter much. What we do know is that when your “about 20% DOD” drops to “about 30% DOD” your battery life will be shorter. And it get shorter for about every 10% it drops.

I hope that answered your question. 


Jan 18, 2009 07:27 pm
Re: Should I use Trojan or Interstate batteries?

When it comes time to replace the battery bank you choose, do ether of those suppliers offer an incentive to take the old ones back with the purchase of a new set? Is there a core charge? A disposal charge? How long has each brand been on their respective shelves waiting to be sold?
One thing is for certain, you will have to replace them one day. You could try one brand this time and the other brand next time. You say one dealer offers both brands.
Even after weighing and counting and discounting and researching until your eyelids feel like they are glued to your eyeballs, it sometimes just takes a leap of Faith.
I have gone from marine deep cycle cranking batteries to, 8-D "big rig" cranking batteries to, Trojan T-105's to, the current set of Surrett 580's. All off grid.
The biggest thing I didn't like about the T-105's was the offset terminal posts breaking off. Thats why I'll never buy T-105's again as long as I live. The cranking batteries well, that was just wrong to start with. So far the Surretts have been holding there own. Its really to early to tell. They have only been in service for 2 years. The plan is to get at least 20 years out of them. Even with the broken posts on the T-105's I got 7 years out of those by the way. I could have probably gotten more years out of them put during the last 2 winters, they depleted very rapidly. It was ether replace the batteries or, purchase an ICE genset. The later I absolutely refuse to do.
Almost forgot!
« Last Edit: Jan 18, 2009 07:30 pm by Thomas Allen Schmidt »

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