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Life remaining in Trojans


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I've been running 6 Trojan 105s off my solar system and original setup.  They have been seriously discharged a few times but seem to be ok now.  My question is this:   how can I determine the life I can expect is remaining in this battery bank?

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I am certainly not an expert but I would think a battery monitor system would be very helpful in determining remaining life.  

My system (three Trojan T1275 12 volt batteries and 750 watts of solar) with a Pentametric battery monitor tells me the efficiency of the battery bank.  Going on seven years of service they still show 96% efficient - about where they were when installed. 

I have never dropped the SOC below 60% so I expect I still have a few years left on them.

The Trimetric TM2030RV goes for around $150.  Might be cheaper than new batteries and always helpful in knowing where your at with your batteries.


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Wet cell longevity is not possible to predict unless they are showing signs of impending failure. (Specific Gravity low)

Maintenance lapses kill most wet cell jars. Excessive discharge is also a significant factor.

If your jars are performing as expected they will likely provide several more years of service with proper maintenance. Using a battery monitor as suggested above will improve your odds.

If after an equalizer charge you see one or more cells with a low specific gravity then their days are numbered, start saving for replacements.

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If you have a 2000 watt inverter and battery monitor, such as the Trimetric, which shows the number of AH (Amp Hours) used you can do this test:

--  Make sure the batteries are fully charged.  Being on shore power for 2-3 days will do it.

--  To be sure your batteries are fully charged let the batteries sit with a discharge of less than 1-2 amps for a couple of hours and check the voltage.  It should be around 12.6-12.7V.  If it lower, say 12.5V, then your batteries are probably damaged.

--  Disconnect from shore power and take a 1500 watt electric space heater and run it through the inverter.  This provides a very constant drain on the batteries. 

--  After using 25% of the total AH of your battery pack turn off the heater and turn off the inverter.  Turn off everything in the RV which uses 12V so that the battery monitor is showing less than 2-3 amps of discharge. 

--  Let the battery pack rest for an hour or so to stabilize.

--  Measure the voltage of your battery pack and compare that voltage to a voltage to battery SOC chart.  Do an internet search for "12v battery voltage state of charge"  to find the charts.

If the voltage of the battery is reasonably close to the voltage for a battery 75% full your batteries should be good for several more years.  On the other hand if the battery voltage is down around the 50% level you are a candidate for new batteries.  However if you only dry camp overnight and don't use a lot of high power devices, such as microwave, coffee pot, toaster, etc those batteries will still serve you for a few more years.

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Al - That was a nice concise way of explaining a method to determine relative health of a battery bank. I also thought your advice about if its below 75% SOC, say closer to what you mentioned at 50% SOC voltage level - it does not mean for a non heavy boon docker, that you need to immediately replace the batteries. 

I had a very similar conversation when I was examining my to me 5 1/2 year young bank of Lifeline X's 4 L16's. My testing indicated that yes I had damaged the bank, and they were down to about that 55-60% level range, using the 75% example above. (I did not do it that way, but the end results were the same, that I knew they were not where they should have been.). I explained to my DW that we could realistically limp along with the reduced capacity for probably another 12 - 18 months without much risk. We'd need too start becoming conscientious about conserving power while off grid. Working with Lifeline, they made me an offer I could not refuse, so I elected to replace the full bank with the same battery. (And, we do not like to conserve power. We did oversize our battery bank so we would not need to do so. And when my DW heard this would also mean Revere Pot percolating coffee in the AM, vs running our electric drop from battery power - well, I could see I was reaching into an uncomfortable style of boon docking for her:)!). But for many who go park to park, or occasionally one or two days at a time without shore power. And are also not in a place where early AM running of the generator is an issue too - just because a battery bank is not as strong as it was when new, does not mean you can't continue using it. (I'd rather have a flashlight with weak battery provided light, then no light at all!). 

My long winded post was to thank you for your nice easy KISS approach for simple relative battery health checking:)! 

Best to you, and all,


PS: I've share this here as it happened. But my abuse to my battery bank was due to bad choice of charging setting parameters between my Magnum MS2812 and my Solar MidNight Classic 150 controller. While in storage, where due to heavy shading of the solar panels, and the way  programmed the MS2812 - I 'walked my battery bank down' over the years. Conditioning helped a bit, but they did not de-sulfate the matts enough to bring them back to where they should have been at that age point. I showed I was about 35% into the Life Cycle capabilities of the bank, when I discovered the damage. (If I had not oversized the bank, it would have become obvious much, much earlier...). New bank now properly being maintained with the adjusted settings, after working with both Lifeline and Magnum. And, I've added a periodic equalization into my maintenance routine too. 

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Thanks for the kind words Smitty.

I agree about replacing damaged batteries....It depends on how much you use and depend on your batteries as to just how soon you need to replace them.

Your experience with inadvertently damaging your batteries is why I tend to shy away from the more expensive brands of batteries.  You can seriously damage an expensive battery just as easily, quickly and severely as a big box golf cart battery.   Glad they came though with replacement batteries at a good price.

Edited by Al F
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