Lead-Acid Battery Bank Frequently Asked Questions

 

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1) How often do I need to charge or "top off" my lead-acid batteries?

 

Maintaining your batteries is the key ingredient to ensuring that your battery bank reaches its designed life expectancy. What you may not know is that this typically does not happen on a partial state of charge on most batteries.  So, yes, your PV system may be charging during the day, but that does not mean that your bank is getting a full charge. The rule of thumb here is to ensure your bank is getting a full charge at least once a week.

 

2) How do I know if my battery bank is getting a full charge?

 

It is recommended that you install some type of battery monitor. This equipment helps you keep tabs on the state of charge of your battery bank, every day at a glance.  Many charge controllers and inverters are already equipped with this functionality, but if they are not there are third party devices that can fit the bill.

 

3) What if my battery bank is not getting at least one full charge per week? 

 

There are a few things you can do when you discover that your bank is not getting at least one full charge per week.  You can proactively decrease the amount of energy you are consuming by using some of your loads less.  If you find one or more of your loads is an energy hog you may consider replacing them with energy efficient models to help reduce your energy consumption. 

 

If those two options do not seem reasonable, consider adding a backup generator to your system.  The generator can help to pick up the slack and help maintain your battery bank by assisting the PV system in ensuring the battery bank is getting a full charge.  You may even consider expanding your PV system to make up for the lack of energy that is able to be harnessed and stored in the system.

 

4) If I connect my batteries to the inverter and/or charge controller, can I just turn the system on?

 

Default factory settings can harm your batteries.

 

Many inverters and charge controllers come with a factory default setting for voltage, battery type, and capacity.  Since this is almost always different per each individual system, carefully planning out your own settings is very important.  Consult those manuals!

 

Failure to properly set your battery bank to meet the demands of your PV system could result in overcharging or undercharging of batteries and over cycling of the bank.  Each leading to a shortened life for your battery bank.

 

5) My battery bank has served me well for some years now.  Can I replace my existing system with any type of new battery?

CH Tech contains other products and information you need, so please check it out.

 

Unfortunately It&#;s not that simple. The settings on the inverter and/or charge controller must be considered first.  Before connecting the new battery bank first adjust the settings on your equipment.  These adjustments are made according to the type, voltage and capacity of the new batteries to be installed. The settings on your solar electronics are always done according to the type of battery installed.

 

Skipping over this critical step may shorten the lifetime of your new battery bank. You expect the bank to last 5-7 years, but may be disappointed when you get only two.

 

 

6) Can I mix new batteries into my old bank?

 

In a word, &#;don&#;t."

 

Many of our customers who currently have a battery bank later desire to expand their capacity or in some cases replace batteries that have failed for one reason or another.

 

Mixing different batteries is never a good idea. First of all, mixing batteries which are different in type, size, brand or voltage will not even work. Worse still, it can lead to battery bank failure.

 

If you were to mix a new battery to an old string or a new string to an older bank, the new batteries would reach their state of charge sooner than the older batteries.  This could lead to them boiling.  In terms of longevity, the new batteries will tend to cycle more often than the older batteries.  More cycles equate to a shorter life span for those batteries.  Typically this will not cause the older batteries to die first, but instead reduce the lifespan of the new one you have just installed. 

 

However, let&#;s say that we are working with identical batteries (exact type, size, brand and voltage), you can mix them up when the age difference between the old and new batteries is not more than 6 months. When adding new batteries to a battery bank that has been used for approximately 6 months or less, your new batteries will tend to adopt the age of your current battery bank.

 

7) When are batteries eligible for the ITC?

 

In short, for energy storage to qualify for the federal ITC the battery bank must be charged by the PV system onsite. If routinely less than 100% of the energy used to charge the battery bank comes from the grid and not the solar this will prorate the ITC incentive.  In other words, "if 90% of the storage charging energy is derived from solar panels, then the storage is only eligible for 90% of the ITC."  Particular attention must be paid to the energy used to charge the batteries in the first year.  "If the solar charging energy remains about 75% buts falls below the percentage established in the first year, then a proportional amount of the tax credit claimed in the first year must be recaptured."

For a more in depth analysis of energy storage and the ITC see Susan Kraemer's article in Renewable Energy World HERE.

I talk about the idea of rejuvenating Lithium Polymer (LiPo) batteries that we find in common electronics, although the thread itself is about Palm Pilot PDA's.

Here's some thoughts on rejuvenating Lead Acid batteries. I am specifically talking about Sealed Lead Acid (SLA) batteries of the type that power alarm systems, backup lighting systems, even trailer brakes, and motorcycles. I've been enticed to get into these experiments as I've bought SLA batteries several times which were new but didn't live up to their name plate rating. Batteries in stores sit around for way to long, maybe years. For some NOT fun, try explaining to someone at a battery store why the little cube battery you bought doesn't work even though their volt meter shows it's fine. These techniques can work with car batteries too, but are a little harder to implement. I'm not discussing anything about adding water to batteries but only maintenance free batteries. I did find some good information on YouTube, and lots of not so good information. So, you have to look at lots of info to know what's credible. You could search for rejuvenating lead acid batteries or desulfating lead acid batteries. I'll give anonymous credit to the helpful YouTuber's I found since I can't recall their channel names at the moment.

As I understand it, lead acid batteries hate sitting in a discharged state. Lead sulfate crystals form on the plates and increase the resistance. That means it's harder to charge and, when you discharge it, you get less energy out before the voltage drops too low. Many batteries are rated at the 20 hour discharge rate. Interestingly, you get less energy out of the battery if you draw the energy out faster. So, if it's a 5 AH battery (theoretically but not actually 5 A for 1 hour), then if you draw .25 A for 20 H, that's your 5 AH. The "C" rating is the same as the AH rating but without the hours. So, for the 5 AH battery, 1 C equals 5 A. You can generally charge these batteries at about .3 C. For the example battery, this would be 1.5 A. You can discharge at different rates but higher rates risk overheating the battery and, as stated, give lots less energy. I've found that discharging at the 5 hour rate, or .2 C gives about 85 % of the energy as doing so at the 20 hour rate or .05 C. Check battery label or specs for specifics.

You can charge one of these batteries with a standard constant voltage constant current lab power supply. This gives you more control over the process than with an automatic charger. If you're going to be closely watching the process, you can set the voltage to 14.7 V (in the case of my 5 AH trailer brake battery). If not watching so closely, set the voltage to 13.7 V (this is the float voltage shown on the battery). Then set the maximum current to .3 C, which is my case is 1.5 A. You connect the red positive lead of the power supply to the (usually red) positive terminal of the battery. You connect the black negative lead of the power supply to the (usually black) negative terminal of the battery.

If the battery is working normally, the current will immediately jump to the max of 1.5 A and the voltage on the power supply will reduce to whatever it takes to keep this current flowing. The voltage will gradually increase as the battery charges. Eventually the voltage will hit its limit of 13.7 V or 14.7 V. Then the current starts decreasing. I would consider terminating the charge when the current reaches 1% or .01 C, 50 mA in this case, or possibly .5 % or .005 C, or 25 mA in this case. Don't leave the battery at 14.7 V for a long time. Leaving (this particular) battery at 13.7 V should be safe. Do not charge the battery unattended until you've verified that it goes through a cycle with no problems. Monitor it for overheating. Do not leave it at 14.7 V.

To drain the battery, I use a microprocessor controlled electronic load tester East Tester ET that I got from Amazon. This is a Chinese unit of pretty good quality. I think it was about $ 200. If you want to spend more, you can look at a Rigol product. If you want to spend way more, you could look at Tektronix or HP, etc.

It's not draining a lead acid battery that kills it as some believe, as long as you stay above 1.75 V / cell or 10.5 V for a 12 V battery. It's letting it sit in a drained state and having lead sulfate crystals form inside. To drain the battery, I set the load bank for constant current mode and set the current for the 5 hour drain rate of the battery or .2 C. For a 5 AH battery, this is 1 A. I set it to drain the battery down to 10.5 V. If it's working properly, I expect to see about 85 % of the name plate rating when I'm done. Remember, they're usually rated at a 20 hour rate. After running the drain at the 5 hour current, I'll run it at the 10 hour current (500 mA in this case) and then at the 20 hour drain current (250 mA in this case). Eventually, I'll get around to doing a charge cycle and a drain at the 20 hour rate to check for rated capacity. If the battery has its rated capacity, great. But, in my experience, they almost never do. A battery is generally considered at END OF LIFE it it's at 80 % of rated capacity.

But, you can often bring them back from the dead. Based on watching lots of YouTube videos, the consensus is that the magic desulfators generally don't work. There may be exceptions, but what you need is physics, and TIME. What may work, if the battery isn't internally damaged, is to simply charge it and drain it repeatedly. This may take 5, 10, or more cycles. As I said in the other thread linked above, batteries are weird and they have weird aging processes. Once you drain the battery and the load bank cuts off, the voltage on the plates rises again and you can run the load bank again for a while. So, I'll drain the battery at the 5 hour rate. A little while after the load bank shuts off, I'll start it again, and drain a little more energy out. Then, I'll do it again. Then, I set it to the 10 hour rate and do that a few times with the same battery. At this point, the battery is almost dead so it won't take 10 hours, maybe 1 hour, maybe a few minutes, etc. Then I set it to the 20 hour rate, and do that several times. Note that I'm not charging the battery, just restarting the load bank at lower and lower current levels. Once I consistently get almost no run time at the 20 hour rate, I get ready to charge the battery again. I note how much energy I got out of it on each of the main cycles.

Then I charge the battery again as noted above. I keep a note card with it and record each procedure. If I'm watching it, I charge it at 14.7 V. This pushes higher current into it (still limited by the constant current setting) for a longer time. This may help reverse the desulfation process. I do NOT leave the battery charging unattended at 14.7 V. If I'm going to leave, it's at 13.7 V. Again, note that the power supply will drop the voltage initially to maintain the constant current that was set. I do not leave the battery at all until I know it has successfully charged one cycle. If it starts getting hot or some cells start getting hot, I discontinue charging or reduce current. This is not a set it and forget it process.

I keep draining and charging the battery until I've reached 10 cycles or until it's performing at about 95 % or better of its rating. This is time consuming. Even though much of the process is automated, moving the battery from the power supply to the load bank and setting things takes some time. I've done this to several of these small SLA cube batteries. I've increased their capacity from 50 % to over 95 %. Once I've rejuvenated them, I put them on a "Battery Tender" 800 mA automated charging and maintenance device that maintains them at a float voltage. Note that I use the Battery Tender for maintenance, not charging.

You might say, why go to all this trouble? Just go get the battery replaced. Well, it's not so simple. As I said, the people at the battery store will pop a volt meter on it and say, it's showing 14.5 V or whatever. The battery is fine (even though it's not). They're resistant to do a warranty replacement. By the way, they also won't warrant them below about 10V. Also, it's likely that the replacement battery has been sitting on the shelf or in the warehouse just as long and will have the same problem. For some of these batteries, which I just use for experiments and maybe lighting when the power is out, they're not too critical. But, for my trailer brake battery (the 5 AH one), I darn sure want that thing to work if it's ever needed in an emergency. So, that's why I do this. Also, I just am curious to know how this stuff really works.

I'm also doing an experiment on one 2.9 AH SLA battery that I cannot recommend yet because I don't know the outcome, but you might find it interesting. As I said, once the load bank turns off, the battery voltage will increase. This battery has been very stubborn in completely discharging. I did the 5 hour drain current with a couple of restarts. Then the 10 hour drain current. Then the 20 hour drain current. Still the voltage kept rising at the end. That tells me it still has more potential energy, even if not much. I INTEND to flatten this battery to 10.5 V (not less). So, I've switched the load bank to constant resistance mode. I'm applying a continuous ~ ohm resistance to the battery down to 10.5 V. It's drawing about 10 mA. Every time the load bank shuts off, I turn it back on. I've been doing this all day intermittently. I'm hopeful that this process is reducing the sulfation internally. Once it really is flat, I'm going to charge it again. I will not leave it discharged.

I'd love to know if y'all have had experience working with batteries in this way.

May your bits be stable and your interfaces be fast. Ron

Hi all. Over on the following thread:I talk about the idea of rejuvenating Lithium Polymer (LiPo) batteries that we find in common electronics, although the thread itself is about Palm Pilot PDA's.Here's some thoughts on rejuvenating Lead Acid batteries. I am specifically talking about Sealed Lead Acid (SLA) batteries of the type that power alarm systems, backup lighting systems, even trailer brakes, and motorcycles. I've been enticed to get into these experiments as I've bought SLA batteries several times which were new but didn't live up to their name plate rating. Batteries in stores sit around for way to long, maybe years. For some NOT fun, try explaining to someone at a battery store why the little cube battery you bought doesn't work even though their volt meter shows it's fine. These techniques can work with car batteries too, but are a little harder to implement. I'm not discussing anything about adding water to batteries but only maintenance free batteries. I did find some good information on YouTube, and lots of not so good information. So, you have to look at lots of info to know what's credible. You could search for rejuvenating lead acid batteries or desulfating lead acid batteries. I'll give anonymous credit to the helpful YouTuber's I found since I can't recall their channel names at the moment.As I understand it, lead acid batteries hate sitting in a discharged state. Lead sulfate crystals form on the plates and increase the resistance. That means it's harder to charge and, when you discharge it, you get less energy out before the voltage drops too low. Many batteries are rated at the 20 hour discharge rate. Interestingly, you get less energy out of the battery if you draw the energy out faster. So, if it's a 5 AH battery (theoretically but not actually 5 A for 1 hour), then if you draw .25 A for 20 H, that's your 5 AH. The "C" rating is the same as the AH rating but without the hours. So, for the 5 AH battery, 1 C equals 5 A. You can generally charge these batteries at about .3 C. For the example battery, this would be 1.5 A. You can discharge at different rates but higher rates risk overheating the battery and, as stated, give lots less energy. I've found that discharging at the 5 hour rate, or .2 C gives about 85 % of the energy as doing so at the 20 hour rate or .05 C. Check battery label or specs for specifics.You can charge one of these batteries with a standard constant voltage constant current lab power supply. This gives you more control over the process than with an automatic charger. If you're going to be closely watching the process, you can set the voltage to 14.7 V (in the case of my 5 AH trailer brake battery). If not watching so closely, set the voltage to 13.7 V (this is the float voltage shown on the battery). Then set the maximum current to .3 C, which is my case is 1.5 A. You connect the red positive lead of the power supply to the (usually red) positive terminal of the battery. You connect the black negative lead of the power supply to the (usually black) negative terminal of the battery.If the battery is working normally, the current will immediately jump to the max of 1.5 A and the voltage on the power supply will reduce to whatever it takes to keep this current flowing. The voltage will gradually increase as the battery charges. Eventually the voltage will hit its limit of 13.7 V or 14.7 V. Then the current starts decreasing. I would consider terminating the charge when the current reaches 1% or .01 C, 50 mA in this case, or possibly .5 % or .005 C, or 25 mA in this case. Don't leave the battery at 14.7 V for a long time. Leaving (this particular) battery at 13.7 V should be safe. Do not charge the battery unattended until you've verified that it goes through a cycle with no problems. Monitor it for overheating. Do not leave it at 14.7 V.To drain the battery, I use a microprocessor controlled electronic load tester East Tester ET that I got from Amazon. This is a Chinese unit of pretty good quality. I think it was about $ 200. If you want to spend more, you can look at a Rigol product. If you want to spend way more, you could look at Tektronix or HP, etc.It's not draining a lead acid battery that kills it as some believe, as long as you stay above 1.75 V / cell or 10.5 V for a 12 V battery. It's letting it sit in a drained state and having lead sulfate crystals form inside. To drain the battery, I set the load bank for constant current mode and set the current for the 5 hour drain rate of the battery or .2 C. For a 5 AH battery, this is 1 A. I set it to drain the battery down to 10.5 V. If it's working properly, I expect to see about 85 % of the name plate rating when I'm done. Remember, they're usually rated at a 20 hour rate. After running the drain at the 5 hour current, I'll run it at the 10 hour current (500 mA in this case) and then at the 20 hour drain current (250 mA in this case). Eventually, I'll get around to doing a charge cycle and a drain at the 20 hour rate to check for rated capacity. If the battery has its rated capacity, great. But, in my experience, they almost never do. A battery is generally considered at END OF LIFE it it's at 80 % of rated capacity.But, you can often bring them back from the dead. Based on watching lots of YouTube videos, the consensus is that the magic desulfators generally don't work. There may be exceptions, but what you need is physics, and TIME. What may work, if the battery isn't internally damaged, is to simply charge it and drain it repeatedly. This may take 5, 10, or more cycles. As I said in the other thread linked above, batteries are weird and they have weird aging processes. Once you drain the battery and the load bank cuts off, the voltage on the plates rises again and you can run the load bank again for a while. So, I'll drain the battery at the 5 hour rate. A little while after the load bank shuts off, I'll start it again, and drain a little more energy out. Then, I'll do it again. Then, I set it to the 10 hour rate and do that a few times with the same battery. At this point, the battery is almost dead so it won't take 10 hours, maybe 1 hour, maybe a few minutes, etc. Then I set it to the 20 hour rate, and do that several times. Note that I'm not charging the battery, just restarting the load bank at lower and lower current levels. Once I consistently get almost no run time at the 20 hour rate, I get ready to charge the battery again. I note how much energy I got out of it on each of the main cycles.Then I charge the battery again as noted above. I keep a note card with it and record each procedure. If I'm watching it, I charge it at 14.7 V. This pushes higher current into it (still limited by the constant current setting) for a longer time. This may help reverse the desulfation process. I do NOT leave the battery charging unattended at 14.7 V. If I'm going to leave, it's at 13.7 V. Again, note that the power supply will drop the voltage initially to maintain the constant current that was set. I do not leave the battery at all until I know it has successfully charged one cycle. If it starts getting hot or some cells start getting hot, I discontinue charging or reduce current. This is not a set it and forget it process.I keep draining and charging the battery until I've reached 10 cycles or until it's performing at about 95 % or better of its rating. This is time consuming. Even though much of the process is automated, moving the battery from the power supply to the load bank and setting things takes some time. I've done this to several of these small SLA cube batteries. I've increased their capacity from 50 % to over 95 %. Once I've rejuvenated them, I put them on a "Battery Tender" 800 mA automated charging and maintenance device that maintains them at a float voltage. Note that I use the Battery Tender for maintenance, not charging.You might say, why go to all this trouble? Just go get the battery replaced. Well, it's not so simple. As I said, the people at the battery store will pop a volt meter on it and say, it's showing 14.5 V or whatever. The battery is fine (even though it's not). They're resistant to do a warranty replacement. By the way, they also won't warrant them below about 10V. Also, it's likely that the replacement battery has been sitting on the shelf or in the warehouse just as long and will have the same problem. For some of these batteries, which I just use for experiments and maybe lighting when the power is out, they're not too critical. But, for my trailer brake battery (the 5 AH one), I darn sure want that thing to work if it's ever needed in an emergency. So, that's why I do this. Also, I just am curious to know how this stuff really works.I'm also doing an experiment on one 2.9 AH SLA battery that I cannot recommend yet because I don't know the outcome, but you might find it interesting. As I said, once the load bank turns off, the battery voltage will increase. This battery has been very stubborn in completely discharging. I did the 5 hour drain current with a couple of restarts. Then the 10 hour drain current. Then the 20 hour drain current. Still the voltage kept rising at the end. That tells me it still has more potential energy, even if not much. I INTEND to flatten this battery to 10.5 V (not less). So, I've switched the load bank to constant resistance mode. I'm applying a continuous ~ ohm resistance to the battery down to 10.5 V. It's drawing about 10 mA. Every time the load bank shuts off, I turn it back on. I've been doing this all day intermittently. I'm hopeful that this process is reducing the sulfation internally. Once it really is flat, I'm going to charge it again. I will not leave it discharged.I'd love to know if y'all have had experience working with batteries in this way.May your bits be stable and your interfaces be fast.Ron

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