It cannot be avoided…
Batteries are arguably the weakest link in the off grid radio chain. Solar panels, controllers, connecting cables, and almost everything else can last years, even decades. But batteries are a consumable product and no matter how good yours are, it’s almost certain they will not last as long as all the other hardware in your system. What are the signs of a battery failure and what can be done about it?
For survivalists/preppers, EMCOMM folks, and anyone else who thinks off grid ham radio is more than just a fun pastime, battery lifecycle is a constant concern. For example, my home solar power system in its current form is about twelve years old. I’ve had the same panels and controller since Day One. Zero issues with these devices. The batteries, on the other hand, have been replaced three times.
So to all the operators who think they’ll just go about their merry way when SHTF: You will be ok, for a while. Maybe even a long while. What about after that? What will be your next move when your batteries finally dirtnap? No plan can last longer than the lifecycle of your batteries.
Another consideration is how much you use your batteries now versus how much they’ll be used in a disaster/SHTF scenario. Batteries have a finite number of charge-discharge cycles. Most operators run them only occasionally for hobby/recreation purposes. If you switch to using them daily for emergency communications, you certainly can expect your batteries to wear out much sooner.
…but it can be mitigated!
Even though all batteries eventually die, there are things an off grid ham can do to extend their life.
Limit depth of discharge: All batteries have a depth of discharge rating that states how far a battery can be drained before damage may occur. Wet cell or flooded batteries have a depth of discharge rating of 50%. Lithium batteries can go down below 10%. Absorbed glass mat (AGM) batteries will only go to 70%. If you repeatedly discharge batteries lower than their respective DoD ratings, you risk permanent damage.
For example, when you buy a flooded battery, you are theoretically getting only half of battery’s rated capacity because it should never be discharged beyond 50%. In other words, treat a 100 watt-hour flooded battery as if it were a 50 watt-hour battery, because that’s essentially what you have. Conversely, lithium batteries, because of their deep DoD capability, can give very close to established capacities. Calculate your battery size appropriately and leave some “wiggle room”.
Increase charging capacity. If you can fill a battery as fast as you drain it, then you’ll be able to pull current for a longer period of time without going below the safe DoD standard . My QRP portable radio kit has a 27 watt solar panel, which is much more than I need to push an FT-817ND radio. By oversizing the panel, I can run all day, even when the sun’s not strong, and barely touch the battery.
Temperature matters…a lot!
Temperature extremes, especially heat, can drastically shorten the life of a battery. Lithium batteries should not be discharged if over 114 F (46 C). Flooded and AGM batteries do not have a specific “drop dead” upper limit, but the hotter they get, the less capacity and lifespan they have. Generally, you’ll want to keep them under 120 F (49 C)
When possible, use a charger with a temperature compensation probe. This device will tweak the charge parameters to allow for temperature changes. While this by itself will not prevent damage from temperature extremes, it will provide a margin of safety and extend battery life. Lithium batteries (should) already have temperature compensation as part of the integrated BMS system.
Battery internal resistance.
One major indicator of battery health is internal resistance. Unfortunately, testing the internal resistance of a battery cannot be done with a conventional multimeter. Basic battery analyzers capable of testing for internal resistance cost less than $100.00. They are well worth the investment
The other hurdle is knowing what a “good” internal resistance should be. The value can vary between different designs and types of batteries. In general, flooded batteries should be less than 10 milli ohms. Lithiums can run up to several hundred milli ohms. This information may be on the battery data sheet. If it is not, contact manufacturer technical support.
If you cannot find accurate data on what the correct internal resistance value is for your battery, there is a work around. When you get a new battery, charge it fully then let it sit for a few hours to stabilize. Measure and record the internal resistance. This will be your baseline. Going forward, you can check the internal resistance and compare it to the baseline. Any significant increase in resistance indicates that the battery is approaching the end of its service life.
It happened to me.
Recently I noticed that my home solar power system’s batteries were dropping excessive voltage overnight. They would charge back up during the day, but as soon as it got dark things went way wrong. I also noticed a funky smell in the air.
I thought the smell might be coming from a sewer, or maybe a mouse got in the house and died somewhere. After investigating, the smell was coming from the utility closet where the batteries are kept. The temperature probe on one of the batteries indicated it was at 100 F (38 C) when the ambient temperature in the closet was about 60 F (16 C).
Of the five 12 volt, 100 amp-hour batteries, one of them went bad, probably from a shorted cell, and was overheating. The resultant disgusting stink was noxious gas coming out of the battery. The suspect battery was at 11 volts, while the rest of the batteries were about 12.20 volts. The one bad battery was sucking all the energy out of the system and pulling the other batteries down with it.
When I checked the electrolyte level in the overheated battery, there was barely any in there. It had all boiled off. I refilled the battery and placed it on a 10 amp charge, taking a chance that it could be revived. After nearly an hour, it was still taking ten amps and starting to heat up again. It was dead for real.
The best I could hope for is that the other batteries were not permanently damaged. I removed the bad battery from the string. After a few hours of strong sun on the solar, it looked like the remaining batteries were going to be ok. I never did conclusively determine what happened to the failed battery. All I now for sure is that the end came quickly, within a day or two.
The moral of the story is that even well-maintained batteries operated within their specifications will eventually go bad.
Make the weakest link a little stronger.
Since all batteries have a finite service life, the best we can do is take measures to extend that life as far as possible. Keeping them within correct operating temperature (which admittedly is not always practical), topping off electrolyte where applicable, and not allowing a battery to discharge too far are all straightforward strategies that do not require a lot of effort or technical knowledge.
Lithium batteries are the best choice for long service life and depth-of-discharge tolerance, but they have a high initial cost. If you can afford the large up-front cash outlay, lithium batteries are less expensive than other types when the cost is amortized over the life of the battery.
No matter what type of batteries you have, be aware of their operating specifications and do your best to stay within them. It may matter when you need them the most.
Special note: Hey everybody! did you know that nearly every article on this blog is the result of a reader question, suggestion, or comment? If you have a topic that would make a good Off Grid Ham article, send me a note on the contact page.
Hey Chris – excellent write-up! If you’re off-grid you gotta be battery savvy, and the points you made are spot on.
Thanks for the support, Rick!
I (think) I finally figured out which way to go regarding the LIFEPO4 battery set up. I’m looking at the Bioenno batteries (only ones I could find UL listed) but not sure about which amp hours I should get.
Looking erlier on Fee Pay, all the 200 watt solar kits I found were from and/or made in China, and had at least a 50 ah battery!! But looking at the charts on the Bioenno site, I should need only about 15-20 ah!!
Same cost (approximately) but the Bioenno is UL listed, and (as far as I know, anyway) a U.S company.
I have a small 10 amp hour Bioenno batter for my portable station and it’s A+. Bioenno support is excellent too.
You are an outstanding source of knowlege. You answer questions I didn’t know to ask.
Thank you for the kind words, Jed. I’m very flattered.
LiFePo batteries are definitely the way to go, at least at this point in time with current technology. If they work as claimed even after 4,000 or more charge cycles they still retain 80% of their original capacity. But damn that upfront cost is enough to make your eyes water. The cost of the inverter, chargers, solar panels, etc. is nothing compared to the cost of the batteries. My wife and I have been looking into putting together some kind of solar system to take some of the load off the grid because our electric bills are running $300+ a month since the latest round of price increases. Preliminary numbers we’ve looked at would indicate a payback time of about 4 – 5 years. But even so I’m still wincing when I look at the battery costs.
Lithium batteries in a large system are still out of reach for most people. But if you can afford it, you’ll do well in the long run.
Excellent information. I believe you’re correct on difficulty testing batteries especially while they are connected and in service. I personally believe the load tester we use for starting type batteries is a poor indicator for a deep cycle and can even cause damage – old type load testers used to have smaller loads than 100a to test different battery types. The battery analyzer really is the way to go by checking internal resistance instead of load output/ voltage. My question for long term battery usage – could you cast your own plates to rebuild your own lead acid batteries? You could store HCL indefinitely as well as lead(which I’m already storing…) Or what are other alternatives after batteries go out in a few years?
I’ve never tried rebuilding wet batteries myself. I’ve heard of it being done but I don’t know how pea it is or if the rebuilds would have sufficient capacity. Hey…you just gave me an idea for a possible future article! Thanks!
Paul, you are correct. The only empty batteries I’ve seen are the motorcycle style batteries that come in the box with the acid separate. I do remember *long* ago buying a vehicle battery and the parts store filled it at the store. I have heard there are some sources for unfilled batteries but never heard of unfilled DEEP CYCLE batteries.
Lithium batteries store quite well if put away at around 50% state of charge. I believe that is true whether it is one that runs your power tool or the bigger ones for solar. Check ’em every other month or so. But that isn’t easy b/c their voltage discharge curve (LifeP04) is so flat that you don’t know whether they are 30% or 80% with a voltmeter. And the bigger LifeP04 stuff hasn’t been around long enough to even validate their warranty period as marketed. Let alone spending mega $$ and putting them on a shelf just-in-case.
Anyway, we are off grid and started just about the same time as Chris – there must’ve been something in the air (wink). Our first and second banks of batteries were those big, heavy 6v Trojans. I was anal with maintenance and charging practices and they didn’t have a hard life per depth of discharge. Never over discharged them – the inverter was set to shut down at just under 49v. And they were always fully recharged each cycle. But I just couldn’t get 5 years out of them.
I got fed up in every way and bought 4ea 3.8-48 lithium blocks over 2 years ago. Life relative to batteries couldn’t be easier. I don’t do anything other than fire up the generator if they start getting around 40% SOC and even then I don’t charge them all the way unless the panels are covered with snow or we are clouded in for a few days. And, actually, LifeP04’s prefer not being charged all the way up. As for warranty ours are warranted for 10,000 cycles at an 80% depth of discharge starting from fully charged. We never fully charge them nor do we take them below 40% so I’m not sure if the internal Battery Monitoring System in each is even counting.
There is so much more I could say but I’ll end with this: If really hurt when I paid for them two years ago. At this point I recall the discomfort but that is long gone and I can spend my old years thinking about other things than battery stuff. I’ll let y’all know what the ‘consumable’ turns out to be.
What is the best tool to use to measure the state of charge of a LiFePo4 battery?
There is only one tool I know of: an amp hour meter. It uses a shunt installed in-line, and when set up correctly it will tell you how much of your capacity remains. As a bonus it will also show the current in-flow (during charging) and out-flow (during discharge) in amps. I have a couple of them in use; my choice was branded “AiLi” (Amazon product #B07FGFFHC6).
Thanks Rick for the recommendation. I am looking at the amp/hr meter you suggested and I see that it will give a reading of the % of charge. My question to you is: Will the depth of discharge reading report accurately with a LiFePO4 battery? The discharge curve for the LiFePO4 batteries is quite different from lead acid batteries?
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With a string of deep cycle batteries, I have found that it is much better to have the batteries wired in series, not parallel. When they are in parallel, a weaker battery will draw the others down. But in series they support each other better and equalize better. Also, running a 24VDC or better 48VDC system for a house is much better than a 12 VDC system. The higher voltage can be converted to AC more efficiently and requires lower wire sizes, because you can carry more watts through a wire at a higher voltage (lower amps/higher voltage). When the posting author described the problem he had with a bad battery, he did not mention if the batteries were wired in series or parallel. This problem might not have happened if they were in series.
The same series/parallel issue also applies to solar panels. Don’t wire multiple panels in parallel. Wire them in series and run the system at a higher voltage. Newbies often make the mistake of wiring in parallel. But it is much better to wire the panels in series. You will need a charge controller that takes the higher voltage, but there are many charge controllers that can take over 100 VDC input.
My batteries are wired in parallel, but I tap the power (positive and negative) at opposite ends of the string, which forces the current to run equally through all the batteries.
If batteries are wired in parallel and the power is tapped at the positive and negative terminals of the same battery, that’s when problems occur. The battery closest to the load will discharge more than the others.
Solar panels can be wired in series but only if all the panels are the same wattage rating. If you have dissimilar sized panels, they must be wired in parallel or the entire system will never produce more power than the capacity of the smallest panel (I did two entire articles about this).
As for the “series vs. parallel” issue, there is no “better” option. Each has its benefits and tradeoffs; it simply depends on personal preferences and they type of equipment you’re using.
You’re right, Chris. How the panels are wired is going to depend a lot on the restrictions of the solar charger being used. My system can handle up to 900W input but can only handle 145V. I can’t hook more than 6 panels in series without going over the voltage limits. So to get the maximum out of my 8, 100W solar panels I had to make 4 banks of 2 panels each wired in parallel and then link the 4 banks together in series in order to avoid going over the voltage/amperage restrictions of the solar charger. Generally higher voltages are more efficient but it’s going to depend on the charging system’s limitations.
FYI I just wired in a manual transfer switch on the house and for the first time in a long time I had to go out and buy wire. Dear sweet lord the wire prices! Fortunately I didn’t need much.