🔋 Battery Bank for solar and generator

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(Andrew) #1

Continuing the discussion from Solar power advice?:

Okay, we have been churning through 12V batteries. We killed 3 smallish SLAs first. They were purchased at varying intervals and died at varying intervals.

We then purchased a regular ole 12V deep cycle marine battery. Someone then wanted to add to our battery bank, and purchased the same 12V marine battery to add to the tiny bank. Those batteries were purchased 16 months ago. The water levels are good, they have never dropped. However, they are down to charging in 20 minutes and running for under an hour with light draw (under 100W).

There are many potential reasons forthe short life. In general, we have been hard on batteries in terms of cold, usage cycles, and charging.

The advice I have received is that we should be running 6V batteries in series-parallel rather than 12V in parallel. I understand this is recommended, but do not clearly understand why.

We have now replaced a faulty generator and a faulty charger. The charging in winter is via a NOCO Gen2 charger providing 12V @ 10A x2 banks (20A total = 240W nominal). Charging in summer is via Renogy 100W solar panels x2 (200W nominal).

What are recommendations for the most bang for the buck batteries?

Currently, I am considering 4 of these…

They are 6V deep cycle “golf cart” batteries. Reasoning: not much. They are available in Fairbanks, which is a difficult market to shop in. Frankly, 4 of them is out of our current budget, but I can’t get any work on this project done without a functional battery bank.

So, I guess I am asking for reasons why I should spring for these.

Also, is there a good alternative for 12V x2 deep cycle that is more economical? All of the options I am currently seeing are hybrid starting and deep cycle. This seems like a bad option.


(BenSpiritbear) #2

I’m no expert but I have read up on solar a bit over the years. I know that car and even marine batteries just aren’t designed to take the use and charge of a solar system. Under normal use they rarely are discharged very much. With solar they are being drained and recharged regularly and they kills them quickly. Golf cart batteries are a good place to start and are a much more affordable battery than solar system batteries which can run $200-$800 a piece. I know the lead cells are thicker and can handle the discharge better. Since you don’t have a big system with heavy use I would think they would work fine for you. From personal experience about a year with a regular battery is about all your going to get.

(Shodo Spring) #3

About 30 years ago, I had a solar array (4 panels) and battery backup. Went to https://www.interstatebatteries.com/. Well, there was no internet then, I went ot the store. They recommended golf cart batteries. I bought the bigger, more expensive ones (not $200 then) . They lasted a few years, charged incredibly, and were not enough to handle the unevenness in light. The second winter, I didn’t keep the water filled up and it ran way down. And we didn’t have a charge controller on them, which is why the water ran down. We could have at least put a light bulb or two in their box, to offer a little heat and drain off some surplus.) They still limped along for another year. If we’d been living there, we would have supervised them better.

This is not extensive experience. But I recommend either solar or golf cart batteries, nothing less; have a charge controller, make sure you don’t run out of water, and maybe add a heating device unless the batteries are in a heated space.


Going with six volts is best because when you lose a cell, you can replace a single battery for half the cost. Two 6v trojan t-105re’s in series is 12v 220ah, and costs about $225 for both batteries. If a cell goes bad in a comparable 12v, you have to replace the whole thing. Really though, I’ve found it’s just bad juju to add batteries of different ages to the packs. If you lose a cell or a whole battery goes bad, it’s best to repurpose the other batteries from the bank, or build them into an auxiliry bank that’s only connected to the main bank when charging or under load using a battery isolator, and replace the whole main bank. If they’re not balanced and won’t balance out, voltage and capacity wise, they’ll just fight each other to early deaths.

I highly recommend at least four Trojan T-105-re 6v batteries. Putting 200 watts of charge at a 440ah 12v pack is an appropriate charge rate. Putting that same power to a pack half the size will reduce battery life by a third. When deep discharged, lead acids like a long time at a low amperage. Chargng them fast reduces lifespan drastically.

Deep discharging also kills batteris fast so a bank sized such that it never gets below 60% discharged, or around 11.5 volts, will allow the batteries to last for years.

Storing an uncharged battery will kill it dead, fast, as will using a barely charged battery in low temperatures. If you can make a little add on to the cabin that holds the batteries, but vents them to the outside, they should stay a little warmer and last longer.

I highly recommend the trojans over anything else. The eight batteries I bought in 2008 are still in service after running a solar powered mobile machine shop for two years, running a window mount ac and a music studio in an rv for three years, and running a beach house in baja since 2015. They’ve always been on an auto watering system, and I wired the pack so the load is equalized across it instead of connecting both inverter leads to one battery.

With lead acids, it’s also possible to extend the life by totally discharging them every six months, charging them up backwards and using them that way for a few weeks, then discharging them and charging them back up in the normal direction. This procedure helped the batteries in old submarines last for 10-12 years instead of 2-3.

Here’s an open source desulfating charger that actually works well. It wouldn’t be too hard to add the desulfating circuit from da pimp to consumer chargers either.

As stated above, a decent mppt charge controller is an absolute necessity for keeping batteries healthy. This is the only one of the affordable ones that I’d spend money on.


Back in the good ol days, Interstates were some of the best batteries out there because they kept using pure lead for much longer than their competition. Sadly, these days, pretty much all consumer level batteries are made with recycled lead that’s full of impurities. Good ol cost cutting plus planned obsolescence.

(Andrew) #6

No budget for two T-105s, let alone 4, so it doesnt matter.

The batteries are inside currently. They don’t usually get below 40°F.

It’s either 4 inexpensive flooded 6V, or 2 similar 12V deep cycle of I can even find them. There’s no budget for those options either, but there is tiny sized money I can take from other projects.

I need to be able to work on publishing projects this winter, and need something to get by until that yields some payoff.

(BenSpiritbear) #7

I have heard you can sometimes find used battery backups used to for servers pretty cheaply and they work well. I know nothing about how to do this or if this even correct information. Maybe @Ernesto would know.

(Andrew) #8

Not shooting down the idea, just a reminder of our context with the nearest town having a population of 80, and Fairbanks is something like 35,000. We have no car to get to or explore Fairbanks and nowhere to stay when we get there. I love creative ideas, but experiments have proven difficult and expensive with location, transportation and lodging challenges.

(BenSpiritbear) #9

I thought of that too but wondered if that’s something we down in the 48 could look for and send them up to you in the spring. Would still have to buy batteries now but wondering if they could be a long term plan. Also not sure what shipping would run on heavy batteries. I think in your situation the golf cart batteries are the best solution if you can come up with the funds.


I looked up t-105’s for an install about a year ago and they were a little over a hundred bucks a piece at the time. Finding the best price definitely took some searching though, and it sure wasn’t amazon. It might have been a bit lower because the order was for 8 of them. It seems like everything on amazon costs about double what can be found with some search-fu.

I know that being up in Alaska makes things difficult but I’m pretty sure that the t-105’s are still one of the most popular off grid batteries out there. I haven’t researched the local market though. I only recommended them because I know they work, and in the long run, are much cheaper than replacing crap batteries every few years. The environmentalist that’s left in me makes me an equipment snob in a lot of ways. I’d rather go without until I can buy stuff that will last than cause even more damage in the long run by buying disposable stuff.

There are always compromises though and I have heard good initial impressions of the duracell deep cycles amongst the az nomads. I’m just not sure about their longevity or how they’ll handle the cold and long deep discharge cycles.

I also think that there are enough cats out there to support your efforts that worrying about a few hundred bucks really shotldn’t be an issue. It just might take some time to herd them. I know that I’d set you guys up with a decent battery bank in a heart beat if I wasn’t in the situation I’m currently in. That situation could change any day now and that keeps me going.

As far as the used server battery thing goes, it can be a crap shoot. Most big corporations replace their backup batteries every three years. Most of the batteries they use last between three and five years, and after three years, their capacity is reduced to 50-75% of original capacity, so best case scenario is you spend half of what you’d spend buying new batteries that last five years to buy batteries that might last two with less than half of the capacity and output on average. The math just doesn’t work out.

(Andrew) #11

I’ve been herding cats for 5 years of this project. I don’t have it in me to keep doing fundraisers every time stuff breaks. The Patreon campaign was intended to smooth out those funding dips. It has been massively helpful in covering the bills for communications and web hosting, but it hasn’t yet generated a surplus to roll back into expenses like this. I keep hoping someone who cares about the project and has a personality required for ongoing fundraising will step up and take that over.

Realistically, I am better at writing and producing content to generate income than I am at fundraising. If I spent as much time with the former, the latter probably wouldn’t be an issue. Not coincidentally, this attempt to get the power situation handled is part of the effort to refocus my time and energy on things I’m better at.

(Shodo Spring) #12

Darn! Lead should be recycled, for all our health. Sorry to learn this.


I’ve been trying to figure out which of my skills is the most worthy to pursue for a while now and most of them have been rock/hard place dead ends but it seems like things are going to change for the better this year.


I used to be genuinely concerned about stuff like that but realized that our loss of our health, peace, and freedom is the price we pay for civilzation, whether we want to or not, whether we voluntarily participate or not, and our sensitivity to lead exposure is just one of Nature’s many tools to get the population back in check. Everything will work itself out in the end.

(Andrew) #15

Forgot to take a picture before shoving them in a dark corner. A part-time neighbor happened to be coming out to his cabin and offered to bring batteries, so we went with what we could get.

4x 6V. The same as those originally pictured.

(BenSpiritbear) #16

Those should work a lot better for you.

(Andrew) #17

It appears these batteries are toast after only a few months despite babying them like crazy (new charge controller, new battery charger, never letting open curcuit voltage drop below 12.3, checking water every 30 days, etc.). They’re under warranty, but the retailer pulled out of Alaska, so more money down the drain. Really frustrating because our neighbors have had their bank with the same cells for almost 9 years now.


They can likely be serviced. I just fixed a 70’s 6 volt motorcycle battery with this procedure and have done many batteries in the past.

Drain the electrolyte into a sealable plastic container. Rinse the battery out with distilled water a few times. Grind up 2 tbsp of sea salt for each cell. Fill the cells with distilled water. Add the salt to each cell. It’s going to offgas so make sure you’re upwind. Once it’s quit reacting, replace the caps and shake the battery as much as you can. Strapping it to a snowmobile or in a truck bed would work. I tape a sawzall with no blade to them, set the trigger lock, and walk away for an hour. It’s gonna leak a little so make sure it’s ventilated and in a safe place. Once it’s been shaken up really well, dump out the salt water while shaking to dislodge and drain the remaining sulfites/dendrites. Rinse with distilled water a couple more times, pour the old electrolyte back in, and charge the battery with a desulfating charger if you can find one. There are lots of diy build tutorials online.

Worst case scenario, the tops of the batteries can be removed and the lead plates can be physically cleaned. A hacksaw blade ground to fit in a sawzall works well to get inside and a variable temp soldering iron can be used to plastic weld them back together.

I feel like I may have posted this but the Navy used to used lead acid batteries in their submarines. Every six months, they’d completely discharge the batteries by running them down then fully discharging them with light bulbs as resistive loads. Then they’d recharge them in reverse and run them backwards for the next six months, then repeat. Reversing the direction of use tends to pull dendrite formations back into solution and some settle in the bottom of the battery instead of shorting the plates. I did this religiously with my Trojan T-105’s and they were still putting out 90% capacity when I sold them, after using them for 6? years.

Basically, if you have clean metal, in acid water, in a sealed container, you’ll have a decent battery. It’s sad that they’ve become such a consumable item.


Also a good idea to get one of these if you don’t already have one:

If the batteries are freezing, that will definitely affect capacity and life too so that’s something to think about. It’s better to discharge them constantly by using a little of their energy to keep them warm than to attempt to keep them topped off all the time and use them cold.

(Andrew) #20

Well that’s sorta good news. Of course, we’ll have to build a still to make the water, and by the sound of it, buy/build a bunch more stuff, but it’s something.

We just had all the tools and cold-weather/hunting gear looted from the boat 2 nights ago, so you’ll have to forgive my temporary lack of enthusiasm.