Battery Longevity - Life Span - Recurring Costs in Solar Power

When I've been researching batteries it seems you tend to get what you pay for but in

most cases each battery type still has a predictable life span on the order of a few years

up to several years. If these deep cycle batteries decline in effectiveness after several years

then the cost to either add additional batteries (is this frowned upon) versus replacing batteries

must be considered.

There are definitely individuals here who are using Harbor Freight Solar kits and their close

relatives to build rather large systems - which means a large number of batteries - or even

multiple battery banks. This thread is directed at these individuals who have been running

large setups for several years.

I'm particularly interested in your experience with the decline of your battery banks and what you

do to compensate for the reduction in efficiency over several years. Maybe my concern regarding

the decline in effectiveness is unwarranted and you've been running a large system for ten years

and never had a problem.

Or maybe those serious individuals (still having fun though) have planned from the start to retire

and replace batteries on a certain schedule. So I'm curious how many individuals start out knowing

they will need to replace their batteries after several years and budget for this cost.

Hope this sparks some discussion and maybe generates some best practices for design and

maintenance of solar battery banks.

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I am curious what members like Big Moe have to say here about replacement cost and schedule. His "two volters" [check em out] are going to cost a pretty penny. Another reminder that there is nothing free about free solar power.

Battery cost is one of the most discouraging aspects for the first timers. But it is the first timer who seems to expect to much from their battery and their system in general. Only after ruining batteries to we learn never, never, ever let your charge levels breach the 11.9 - 12 volt range. If you don't you will get many years of service out of your batteries.

I understand most inverters (and even the Harbor Freight charger/inverter unit) will shut off when the voltage

gets down to a certain level. When you say folks learn after ruining some batteries - is this because they are

bypassing these devices with built in safety mechanisms? Like bypassing the protected inverters and

running directly off of the battery. Or are there ways to kill batteries even when using devices that are

supposed to protect the batteries. At this point I've been assuming the charger/inverter are intelligent

enough not to destroy my batteries.

Batteries left without incoming charge will lose a charge, a little at a time. How long are you talking? It doesn't take much to keep them charged. Surely where the panels/batteries are located hasn't been plunged into absolute darkness, has it?


    Bill here, I woulded loose sleep if this is the set up we talked on back a bit. The batteries forsure will loose charge when not in use, very little over short time periods.As to maintaining the charge the panels should be able to handle that. As to snow, a few day is what it takes to dig out here in the woods of Minnesota, and I use a front end loader! I would advise you keep an eye on the panels being burried under snow, long term! A few days is no big deal.  

I would have to agree that there isn't any free power here. It seems folks also forget to consider the changes and failures that can and do happen. I have a larger battery bank that replacement has been considered in the systems break even point. It also needs to be addressed that equipment failure and replacement happen, say an inverter failure?

  Heck, my system started as a simple 90 watt toy, A toy that soon will be over 2000 watts??    

You've got a large system and I suspect a lot of money invested in batteries.

I suspect the design of the system relative to load will have a serious impact on the life of the batteries.

That is, if the system is under-designed for the load and the batteries cycle a lot, the batteries will not last as long.

So do folks over-design their systems so that the expected load does not completely drain the batteries frequently. Does your 2000 watt system easily support your load or does your system drain and shutdown when it hits low voltage?

  I've been planning on replacing batteries every four years.  When I started the system up, I had two deep-cycle marine batteries out of my hearse, one four years old and one five.  The younger battery was still good, the older one shot, so I thought this would be a good place to start.  If they start failing sooner, or later, I'll change it.  I use those big 115-Ah marine batteries from Wal-mart, and they all have month/year stickers on them, so it's easy to keep up with.


  As to the cost of batteries, yeah, real problem.  I use a GTI for my big panels, just to get the maximum $$$ out of them, while amassing more panels.  I'm putting about $50 worth of power on the grid per month this time of year, but my Internet equipment, laptop, security lighting, and some of my indoor lighting is all 12v, so if the power goes, at least I have that.  I'm also considering the possibility of linking an APC 1500 UPS to a GTI and seeing if it will synch up.  It might be possible to create my own little grid here, in the event of a power failure, and have the GTIs come up in synch with the full wave that the UPS creates.  It might work, maybe not, maybe fun to try this winter when I get bored.





   Bill here, I'm useing 1160 amp hr's on the golf cart batteries, I got a true'r deep cycle battery and amp for amp a great buy! There life span is expected to be 4 to 6 years in the carts IF TAKEN CARE OFF!

  I'm in the north woods and this time of year have more power then I truely have a place for, WORKING ON THAT! But come winter everything slowsdown, a fair share! I do not sell to the grid, they pay less then half of what the sell for so it more cost efficient to use it on site. I am set up so my 120 branch curcuits can be switched from solar to grid power with the snap of a switch. Summer we try to use it all, winter grid becomes my back-up. Upon a grid power failure we can snap the switches and start being conservitive, but have power pretty much as needed, less the large loads.

Reading Bill's comment made me think that we should find someone who works in maintenance at a golf course and ask them "what kind of life are they getting out of a good 6 volt battery".

New project, anyone?

   Mr Ray

   Bill here, I did exactly what your asking when I got my batteries. I have a distant friends that owns a gulf cart shop. It was he that told me to figure on 4 to 6 years possibely more as the demands Im placeing on them is low and with the continuses tempreture that they really should do better. They also advised lack of care or deep discharge would make a year or two be there end!

   Dollar for dollar I didn't pay a lot more per amp hour then marine deep cycle batteries and these are true deep cycle that should have a longer life.


Hello David,

This is a huge factor in the cost of the overall system. When I went into the 2 volt batteries it was with the understanding that they have an 8 - 10 year life if they are cared for.  I'm currently on year two so I don't have much data as of yet. I do plan on replacing them, but my hope is that by the time they are at that point there will be a better battery out there.


For the money the lead-acid RE batteries from trojan seemed to be the best bet. They are rated for the longest life I could find an even though there are newer technologies for batteries (AGM for one) they do not deliver the AH that they more improved and tested lead-acid's do for this type of useage.


As for how to deal with the declining output... for me it is an easy answer. I continue to grow my systems input to the bank. I am adding more power sources (wind generators , different types of panels - poly and mono - ) to keep constant power coming in. This helps overcome a diminishing return. I plan on adding a second bank of batteries as I go forward. This will not be connected to the first bank because of age differences. This bank will also be a 24v bank and will power 24v inverters.


I did start out knowing that the batteries are the most costly and the least durable part of the system, but independence has a price. One that I felt was worth paying for.


At this point I can not answer your question with much confidence, once I have a few more years under my belt with these batteries, I can throw out more data.



     Mr. Moe

   Bill from the woods here. I choose the gulf cart batteries basically as a compromise, cost verse's what I truely want! However, in my younger days early 60's an older friend introduced me to the green power idea, we didn't no it was green back then! He bought old wind generators, mainly the Jacobs plants. They ran usually 1 to 2.5 kw and were 32 volt. The reason I'm telling you this, we reinstalled old lead acid batteries that were over 20 years old and still functional. I'm told this was not uncomon IF THE BATTERIES WERE TAKEN CARE OF!

   I don't recall the reserve sizes or?, but can tell you having hauled and loaded them they were BIG! like a pile 3 feet square buy over 3 feet tall, and those folks didn't run much with them, but realise a radio drew around 150 / 200 watts and worked on heating the room.

   Regardless of battery type the death of a it seems to be largely a result of abuse. Folks expect way to much from there batteries. I have figured on a bank large enough so that the load devided out is small on each battery, charging is the same. Basically I use big batteries and draw small loads against each. Half the battery bank size, twice the work on the battery, return charge to. As the demand raises so do things like temps and ineffiencies. Those are what kills small banks with large demands asked of them. It seems everyone buys a marine deep cycle and a big inverter thinking they will get by, but you can't beat the math! A reliably system has to be figured and balanced. I have yet to be without power, I did do a lot of calculating and thinking before I started. I infact have excess power in the summer, I'm working on that! But also set up so that in the winter, I'm in Minnesota and the sumer / winter averages are very different , I can switch back and use more grid power. Folks also seem to forget that the grid not just battery can be a great back up. I have yet to be undersized there! And replacement is not a concern. My goal is lower bills, not total independence. I'm letting the grid power my heavy loads, we have a shop on site and other  large draw loads that I'll gladly pay the power company for. But the basic house is getting closer every day to being 100% off grid, but again with the snap of a switch we can repower branches of it to the grid if needed. Yesterday, I infact ordered the gear to beter then double the system size, I do beleave this to be a great sourse of power and the back up is a nice feature!

   On replacement cost against opperating cost, here it's figured in. As to replacement,,, I might do it once then it's someone elses problem as I won't be here!

    Folks however also forget  to consider in there true cost, had they taken the money invested in equipment and put it in the bank drawing interest and bought grid power the potential interest pushes the pay back out even further, NO FREE RIDE HERE! The true cost of a system is high and truth be known I probably am paying more per kilowatt for my free power then a kilowatt of bought grid power? I'm hearing that grid power price's are  due to go up soon, that will help shorten that return!

   One last thought, do you suppose the goverment is going to soon make us register our panels? It has to dawn on some one that this is power without tax! The only way I can see them recovering what we used to pay, realising more are doing this every day! will be to start mettering us or find panels and tax us for the output.

   If you think I'm extreme try this thought. Lets all buy and run all electric cars. There is no road tax on that power when you plug it in at night, or worse use solar and wind to charge it. How now do we maintain the roads as we all beat the highway tax? They will be comming its just a matter of how many of us are doing this, the number grows every day and soon it will be enough to draw there concern. 

    Mr. Moe a lot here is no news flash to you, I thought it might spark some thought for others!



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