Useable Off Grid Battery Life

Mangas · February 2008

What battery life have owners of lead acid wet cels experienced?

Assuming normal maintenance, good environmental storage and not kicking them too hard, I am curious about battery life and replacement. I've heard anywhere from 5 to 11 years. I realize it's dependant upon loads and use.

My own off grid system design assumed at least 8 to 9 years at 90%. Was I correct in this assumption?

Solar Guppy · February 2008

Re: Useable Off Grid Battery Life

for the average user, I think 2-4 years is common. Almost everyone under estimates the loads, under charges and has battery banks much larger than the charging source. For every sucess story I read about 20 that didn't have such an outcome

Now, if you do everything right, including topping off, no undercharging, do equailize cycles and don't run the DOD to low, yes its possible to get 8 years from a set. I haven't read more than a couple of people at getting 8+ years

Were all human and no amount monitoring can be done 365 days a year, mr murphy will make sure those few days your not around things will happen ...

icarus · February 2008

Re: Useable Off Grid Battery Life

While I agree with most of what SG says, and he has considerable more experiance than I do, I have a bit of a different result.

I have 2 small off grid systems. The first is a pair of t-105 trojans, powering a few lights etc. I have been very careful with the discharge side, keeping the water up etc. I have never discharged them more than 20% and they get fully charged every day, or two at most. These batteries are now just 10 years old. They seem to be as good as new, but I assume I am on borrowed time with them.

The second system is a full time system that started with 6 l-16 trojans. Once again, never discharging them more than 20%, getting them up to full every day or two. This system is also ten years old. Of the six l-16's one failed after 7 years, bad cell, a second failed in year 9. (In fact I am limping along with the 3 remaining l-16's and the 2 t-105's in a series/parallel arrangement figuring that they all will die at about the same time. At that time, I will replace all with 6 new l-16's and hope to get another ten years. (I hope I can get another year or two out of what I have going.

As Solar Guppy suggests, (and his experiance bears out!) how you charge, load and tend them makes a huge difference. My system has always been over batteried and under PV'ed. I know the experts recommend against this, but I have been able to make it work. I really think that the key is size a battery bank so that you can keep the discharge as small as possible.

Icarus

PS I never did a proper equalization until year 8 on any of these batteries! I also had no good metering capability until year 8! Blind luck plays a role as well.

PhilS · February 2008

Re: Useable Off Grid Battery Life

My first set of T-105s lasted about 7 years with embarrassingly poor upkeep and maintenance. At the end it was a pretty sad looking set. I committed to better care.

My second set of 12 T-105s lasted about 9 years. I had Water Misers on them and a battery desulfator on each end of the bank. I kept them clean. I was actually down to 8 batteries as bad cells had developed in 3 over the last couple of years.

Last month I replaced those with a dozen Batteries Plus store brand ("Werker"). Saved about $300 over T-105s and hope it was the right decision. Transferred the Water Misers and still have the two desulfators attached.

Phil

Mangas · February 2008

Re: Useable Off Grid Battery Life

Thanks everyone.

I think my own system is well sized between the array, battery bank equalized properly and the operating environment for the solar mechanicals is optimal. With luck I'll see 8 - 9 years best case.

I budgeted battery replacement in 8 years.

icarus · February 2008

Re: Useable Off Grid Battery Life

Sounds like a good bet. No matter what happens, the unexpected will!

Icarus

Mangas · February 2008

Re: Useable Off Grid Battery Life

Icarus, you're so right.

That unexpected hail storm I had last year sure had me pacing. I was counting them!

System2 · February 2008

Re: Useable Off Grid Battery Life

I too have so far had very good results with L-16 batteries in spite of not properly looking after them due to lack of education. The education thing has been fixed now, due to the great people on this form, a lot of reading, and experience. The six L-16's that I have, will soon be 6 years old and are still like new, as far as I can tell. I too, only recently did my first real EQ. Until a few months ago, I only had 660 watts PV, now up to 1000 watts through an MX-60, which I LOVE! Always try to never take more than 20 % out of bank. usually only 5 or 10% and like to see them topped up ASAP. I use "Rust Check" spray on all battery terminals and cable ends, and this has kept them all just like new - - NO corrosion at all, none! So far only need water perhaps 3 times a year, and even then it wasn't even half way down to the top of the plates, I just like to see them full. First real SG readings were only taken about 2 months ago and I was pleasantly surprised at the results. All read fully charged and well within range. Would I go with L-16 again? You bet I would, they took my ignorant abuse for years and kept on ticking. Granted, I didn't deep discharge them and I kept the water up, but everything else I did, or didn't do, I'm now ashamed of. In fact, the first almost 3 years of their lives were with my own, home built single stage regulator!
So I've come a long way, and they were, and are like ever faithful, loving dogs.

Wayne

Solar Guppy · February 2008

Re: Useable Off Grid Battery Life

Well, there is no magic here for the happy battery posters, as you all have stated, you don't go below 20% DOD and keep thm watered. From another post I just read on your L16's

L16
exp. cycles % DOD
4398 10
2322 20
1614 30
1266 40
1036 50
884 60
774 70
698 80
633 90
600 100

So if you abuse the DOD, 2-4 years, barely use it, 8+ years. I stick by that most people kill batterys with a lack of understanding the basics of energy in vs energy out and no one posting in this thread qualified as abusing there batterys.

icarus · February 2008

Re: Useable Off Grid Battery Life

The dod chart vs cycles tells the tale. I have always been a fan, (counter to the experts here) of too much battery for not enough load, not enough PV, rather than the other way around. Given a choice I would always start with big batteries and add PV as you can afford, and above all, keep the loads under control.

There's no substitute for capacity.

Icarus

lamplight · February 2008

Re: Useable Off Grid Battery Life

i bought t-105s per recommendation from my dealer, as he literally wrote "the battery book for you pv home" that many PV installers sell around the country (new england solar electric) . with many of the systems he designed / installed still running after 10 yrs. mine so far run fine after 4 yrs which included 1 winter of severe undercharging/poor maintenance by myself, and 3 other winters of just regularly poor maintenance (ie regular top offs). they get regular charges and Eq's throughout almost 3/4 of the year, regular watering all year. i have no illusions ill get 10 years in my particular case but i expect based on their current performance (and the winter abuse/sever dod) to get well over 5 yrs, possibly more if i get myself a decent ac charger for the 2 mos. a yr i could use it on occasion. anyhow, if i'd actually read the battery book or similar i bet id be doing even better

Useable Off Grid Battery Life

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