Connecting Batteries Together
Connecting Batteries Together For More Battery Storage
For either off-grid or grid-connected renewable energy systems that use batteries for their energy storage, connecting batteries together to produce larger battery arrays of the desired operating voltage or 24 hour current demand is an important part of any solar power energy storage system.
Most alternative energy generating systems fall into two main categories, a “grid-connected system”, and an “off-grid system”. Grid-connected systems are so named because they connect directly to the electrical utility grid and if the electrical generating device, solar panels, wind turbines, hydro generator, etc, is producing more electricity than is needed, the excess is fed onto the grid.
But grid-connected systems with battery backup (Hybrid Systems) are also possible. Battery based grid-connected systems require a different type of inverter as well as a battery charge controller to monitor the flow of electricity into and out of the battery bank.
Off-grid or stand alone systems use batteries to store their electrical energy. Off-grid systems are ideal for remote rural areas and applications where the connection to a utility grid is either impractical or unavailable. In these cases, it is more cost effective to install a single stand alone off-grid system than pay the costs of having the local electricity company extend their power lines and cables directly to the home.
All stand-alone and battery backup alternative energy systems whether wind, solar or hydro powered all require some form of battery storage so its important that connecting batteries together is done correctly.
An electrical generator charges the batteries, usually during daylight hours for solar and the batteries supply the power when it is needed, often at night and during cloudy weather, so connecting batteries together to store this free solar energy is and important part of any off-grid renewable system.
The two most common types of rechargeable batteries in use today are lead-acid and alkaline. Lead acid batteries have plates made of lead, mixed with other materials and submerged in a sulphuric acid electrolyte solution. The lead acid battery is an integral part of any off-grid alternative energy electrical system and the fundamental lead-acid technology has not changed since its invention.
Lead-acid batteries are the most common in renewable energy charging systems because their initial cost is lower and because they are readily available nearly everywhere in the world. Deep cycle lead acid batteries are called a secondary battery, as it may be recharged by applying current. A primary battery is one that is not rechargeable. All deep cycle batteries are, therefore, secondary batteries.
Deep cycle batteries are a form of lead-acid battery that is specially designed to provide a steady current over a long period of time. There are many different sizes and designs of deep cycle lead-acid batteries available, all designed to be repeatedly discharged by as much as 80% of their capacity so they are a good choice for off-grid systems. Even though they are designed to withstand deep cycling, these batteries will have a longer life if the cycles are shallower.
Connecting Deep Cycle Batteries
Batteries are generally wired or connected together to produce a specific voltage and amp-hour storage capacity. The batteries of small renewable energy systems, for example, those used to power cabins, RV’s and boats, etc, are typically wired to produce 12-volt electricity.
Off-grid systems used to power homes and businesses, etc, are typically wired to produce 24 or 48 volt DC electricity. This low-voltage DC electricity can also be converted to mains AC electricity by an inverter which boosts the voltage to 120 volts or 240 volts, commonly used to power larger electrical devices.
When more than one deep cycle battery is connected together the resulting battery bank will have either a different voltage or a different amp-hour capacity (or both) when compared to a single battery.
Batteries can be wired or connected together in either series or parallel combinations, or both to increase the voltage or current capacity of the battery bank. Then connecting batteries together allows for more battery storage.
Batteries Connected Together in Series
A battery bank is built up by connecting two or more deep cycle batteries together. Battery banks made from batteries that are connected in series have the same current capacity as the individual batteries, but the voltage is multiplied by the number of batteries in the series string.
In a series connected battery bank the positive terminal of one battery is connected to the negative terminal of the next, and so on. Connecting batteries together in a series combination means a higher voltage for the same current.
Batteries Connected Together in Parallel
Battery banks made from deep cycle batteries that are connected in parallel have the same voltage as the individual batteries, but the current capacity is multiplied by the number of batteries. In a parallel connected battery bank the positive terminal of one battery is connected to the positive terminal of the next with the negative terminal connected to the negative terminal. Connecting batteries together in parallel branches means a higher current for the same terminal voltage.
Series and parallel combinations of batteries within a battery bank increase both the voltage based on the numbers of batteries in the series strings and the current capacity based on the number of series strings connected in parallel. Connecting batteries together in both series and parallel combinations allows for more battery storage at a higher voltage.
Lets look at some of the ways we can connect batteries together to produce higher voltages and current configurations.
Connecting Batteries Together For 12 Volt Wiring
All combinations of series and parallel battery connections will produce an array of 12 volts.
Connecting Batteries Together For 24 Volt Wiring
All combinations of series and parallel battery connections will produce an array of 24 volts.
Connecting Batteries Together For 48 Volt Wiring
Finally, these combinations of series and parallel battery connections will produce an array of 48 volts.
In off-grid stand-alone alternative energy systems, the electrical energy produced by the generating device can not always be used when it is produced. Because the demand for energy does not always coincide with its production, electrical storage batteries are commonly used in many off-grid and grid-tied systems.
The battery bank voltage selection, either 12, 24 or 48 volts often depends on the load voltage requirements of the system, the storage capacity required and the type of batteries available. For larger loads it is sometimes better to connect deep cycle batteries together to produce higher voltages in order to lower the system currents.
For example, a 240 watt DC load operating from a 12 volt battery draws about 20 amps, where as a 240 watt DC load operating from a 48 volt battery only draws 5 amperes, a quarter of the current. This lower system current has many advantages by reducing the size of the cabling, isolation switches and fuses used thereby saving you money.
One final safety point in understanding batteries and connecting together lead-acid cells for greater battery energy storage. Lead acid deep cycle batteries are the most dangerous part of any solar or wind power system. Gloves, eye protection such as goggles and masks as well as old clothes must be worn when handling lead acid batteries and electrolyte as “battery acid” both burns and irritates skin and eyes.
To find out more about “connecting batteries together” and how you can use them as part of a Home Solar system, or to explore the advantages and disadvantages of connecting batteries together for more battery storage and how you can use Deep Cycle Batteries as an alternative to automotive batteries, then why not Click Here and get your copy of one of the top battery builders guide from Amazon today and learn how to build, rebuild and recondition deep cycle lead-acid batteries
Thanks for producing a nice and clear, straightforward language site to explain the ins and outs of batteries and off grid connections!
I have been living completely off-grid for 7 years now. I use Six fairly generic 100Amp/Hr flooded deep cycle batteries in parallel, (600Amp/Hr capacity), connected to a 3000W inverter.
Due to a lot of pre planning and forethought I chose to minimise current draw to a minimum by calculations of all Wattage requirements before even building the cabin. That and the massive outlay for big systems. The maximum draw that I could possibly use is about 30Amp/Hr at 12VDC…but I rarely use even that much.(Very frugal with power and the batteries rarely drop below 80% of full charge or 20% discharge from full).
The Battery bank is charged via 400W of solar panels and a 600W wind turbine, so I have rapid charging in most conditions.
When I purchased the batteries all at the same time from the same batch, I was told to expect 3-5 years of use from them before having to change them all out, and that I would have been better to invest in gel, or even better, Lithium Iron Phosphate…Im on year 7 and not seeing any downgrading yet!
My points of note from my own learnings for others that may benefit…
* Keep batteries well ventilated, clean, and check electrolyte levels at least every other month or so.
*Disconnect all batteries twice a year to check all connections and shuffle the batteries around at the same time.
*Yes, series connections save $, but then you need to configure the solar array for the 24/48V charge controller and Inverter…as well, If you do need to boost or equalize the batteries, you will still have to seperate them all in order to charge each one individually at 6 or 12Volts…So having a 12V parallel set up makes topping up with a 40A car charger much more easy in a rush, and simpler connections to do so individually.
*Build a system that wont discharge much below 30% of full capacity and that charges quickly.
*I will have to change out the batteries eventually, like all types do, but now its become a fascination with proving how long can I get out of my batteries. (They cost me $700 Canadian for all 6, gel would have been $1500 and LiFePhos would have been $5000).
Presently if they went dead on me today, I will have saved $4300 compared to the LiFePhos option, and right now I would still consider flooded deep cycle batteries as a replacement as they are easier to recycle when their life is over and IF a subsequent set lasted only 3 years, then I could continue doing this seven times before I reach the threshold of cost replacement to change to LiFePhos batteries.)
Thanks again and have fun out there!
I have batteries removed from a UPS. 160 batteries in total.
80 x YUASA SWL3300FR 12V – 110.2Ah
80 x YUASA SWL1850FR 12V – 74Ah .
rather than waste, I am looking at using for a solar install what would be the best way to approach this what would i need? etc.
That depends on what you want to achieve. Decide on your battery bank voltage, 12, 24, or 48 volts. Configure your batteries in series and parallel branches to suit. Since the amp-hour (Ah) capacity of a battery bank is the sum of the capacities of the individual batteries, then you would need two battery banks. One for the 110.2Ah batteries and a second for the 74Ah batteries since their amp-hour capacities are different. Then you can source two charge controllers to meet the voltage and Ah capacity of each battery bank and wire them in a balanced charging configuration.
I have 3 100 amphour deep cycle batteries connected in parallel but my powertech battery monitor only shows a reading of 100amphours is it possible to get a reading of 300 amphours. Have I wasted my money. Thankyou Graham Yates
A battery monitor will measure the terminal voltage of the connected battery only, in order to determine its state of charge condition allowing you to keep track of battery performance. For parallel connected batteries, the monitoring of current, voltage and SOC of the battery bank would require a shunt in the outgoing negative line. Since a shunt is a resistive element, when a DC current passes through it a small voltage drop is developed across the shunt which can then be used by a suitable battery monitor to determine the battery banks SOC.
I have three 200ah 12V, two 150ah 12v, and two 100ah 12v batteries. I have a 3000W inverter and a 100A charge controller. The main thing I want to do is cool down my cabin with a portable air condition, run a small fridge, and run lights. What is the most optimal setup?
A 24V battery bank, with two of each amp-hour battery in series and three parallel branches. With such a variation in amp-hour ratings, your batteries will charge at different rates.
I have 32 6v 200ah agm batteries to connect in series and parallel to form 24v. I have tested the internal resistance, CCA and voltage to group them. I have 4 x 20 amp charge controllers. How do I connect the controllers to charge equally. I can’t find any literature on parameters of internal resistance and actual CCA. I won’t use a battery with more than double the internal resistance of what the manufacturer states. The CCA varies, and I have read to divide it by 7.25 to get Amp hours. Unsure how to group them because the internal resistance in the CCA readings vary.
Also use the voltage readings to group. All batteries are 4 yrs old. 🙂
Cold Cranking Amps is of little importance for deep cycle batteries. Ideally, a deep cycle battery should have 0 ohms internal resistance, but there will always be some resistance no matter how small as the batteries plates (electrodes) and the electrolyte used isn’t always 100% conductive. Ohm’s law states that V=IR, so the higher the internal resistance, the greater the voltage drop and therefore losses inside the battery when charging and discharging.
There are different ways to connect a bank of batteries in both series and parallel at the same time. They can be recharged by a single charger having the same nominal charging voltage output as the battery bank voltage. Batteries connected in parallel, should be configured to use only one charger. But batteries in a series string can be charged individually using different charges. For example, two batteries in series, two chargers. However, individual battery voltage imbalance in large series strings should be avoided.
I have 3 -24volt lithium batteries and a 24 volt invertor . Can i wire 3 batteries together and end up with 24volts?
Clearly, if you have 24 volt batteries, a 24 volt inverter and you need a 24 volt supply. Then you would connect them all in parallel
Hi there, I’m quite new to all of this but find myself the owner of (10) 12V 140Ah (amp hour) batteries that for now, I just want to keep healthy/charged. If I understand these articles well enough, I can get a 12V charger, and connect the batteries in parallel, connecting the positive to the first battery in the chan, and the negative to the negative terminal of the last battery in the chain. So far so good? Are there any guidelines for guage of wire for connecting these in parallel?
Since your battery pack voltage is 12 volts which is exactly the same as each of the individual 12-volt batteries. The total storage capacity of the battery pack is the sum of the capacities of the individual batteries. That is 10 x 140Ah = 1400 Amp-hour capacity. Thus if you wanted to charge or discharge your battery bank within just one hour (not recommended) it would supply (1400/12)/1hr = 117 Amperes. Likewise, charge/discharge over a two hour period would be: (1400/12)/2hrs = 58 Amperes, etc.
Cable sizing is a function of the length of the cable and the current (amperage) that will flow through it. Thus the longer the cable, or the higher the amperage, the bigger the cable diameter must be to avoid losses. Then: 1) determine the length of cable from charger/connection point to battery bank with cables connecting each battery of equal size and length as leads. 2) determine the maximum current rating of your charger and/or you expect to draw. 3) keep voltage drops and losses below 5% (12.7 x 95% = 12 volts or greater at cable end).
Then suggested cable sizes range from 6 AWG (16mm2) to 1/0 AWG (50mm2) depending on length and amperage required.
I currently have a 48v system of batteries and want to add another 8 x 6v batteries to this bank am I good to add all together? And what would be the best way to connect them all together
Eight 6 volt batteries connected in series would give you your 48 volts. Connect the series combination in parallel to your current 48 volt battery bank to increase capacity.
I’m also looking at going from 8 to 16 6v batteries will this help my system, I’m off grid solar with generator back up and my generator has been running lots lately
Adding extra storage capacity to your system is always a good idea as it will give you more hours or days of autonomy. However, your existing system must have enough spare capacity to fully charge any additional batteries added to it during the full sun hours
I am off grid for more than 30 years and am I going to replace my bank of T105 (20) for the third time very soon.
I am running a 12 volt system with a 12 volt 1500 Outback inverter.
My question – the answer to which I can not yet find-is the following. If the cost per amp is just about the same, should I use larger amp hr batteries with fewer interconnections, or does it really matter? I suspect that there must be some loss with all the cabling interconnect a 20 T105 entails. And yes, I am using sufficiently heavy cabling interconnect. So to some it up would, it is better to have 10 430 am hr. connected in series or 20 235 amp hr batteries given that the total amp hrs for both configurations are almost the same. The only difference would be the size and weight of the batteries and few interconcencts.
Basically yes, as its generally a good rule of thumb to try and keep the total number of batteries in a bank to less than 10 to 12. If more storage capacity is required, bigger batteries should be used, not more small ones. The number of connections between batteries isn’t generally a problem provided they are clean and tight and less batteries means less watering. Generic golf cart batteries like the T105’s are expected to last a maximum of 5 to 8 years anyway, so it is not surprising you need to change them again.
Also, battery life is directly related to how deep the battery is cycled each time so check the the number of cycles of discharge of your new batteries. For example, 550 cycles to 50% discharge equates to about 2 years of life (50% depth-of-discharge is a good standard value) and they should be recharged again at a rate no more than the C/8 value which would avoid cable overheating. Your charge controller should do this.
I think that another factor – and why my batteries lasted so long- is that the battery bank is large, and therefore it is rarely discharged to a rate of 50%. So the bottom line is -if you can afford it- the most large amp hr. batteries the better. But not more than 10 connected together. I was also told that it is not a good idea to connect many batteries together in parallel. Hence all the 6 volt batteries in series.
There is some correctness about your assumption. For series connected batteries, the same charging current flows through each battery in the series string, therefore the same amount of charge is deposited onto the plates of each battery.
However for parallel connected batteries, while the terminal voltage across the batteries is more or less the same, the charging current through each battery branch will be different, due mainly to the specific gravity of each electrolyte, internal resistance of each cell as well as interconnecting cable resistance. This can result in circulating currents around parallel connected batteries as the higher charged battery tries to charge-up the lesser charged battery as the bank tries to equalise itself after charging is removed. Balanced star-point charging methods eliminate this problem.
I have a 96v battery bank three rows deep,my Batteries are 220ah each, each row in series and parallel at the ends, I have 2 controller’s each 3000w 96v 60A , but they only reach 1 -2 A in winter and when one works they cancel each other out!when above 3.0 amps so only one works! But at low amps they both work! How can I make the sync working together! Also what’s the best battery configuration for my 96v system! What size battery wire should I use? to connect batteries in series as I’m using 6 mm2 .
Clearly the two controllers are competing against each other, especially if connected in parallel as they will not sync together. 1 to 2 Amperes charging current will depend on the state of charge (SOC) of bank and available power being supplied by panels during the winter months of low irradiance.
Then please check your manual for the correct and same charging program/setting configuration for voltage regulation. If the two controllers allow direct communication between themselves, use this to ensure they charge correctly in parallel. Also, each controller must have its own RTS temperature sensor, and the battery voltage sensing wires are the same length and both connect to the same battery terminals.
Try to split the battery bank in half and connect as two series halves of 12 batteries each (assuming 12V batteries) with a center common connection. One controller to feed one half.
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hy i am planning to make a 192v 200Ah li-ion battery using 18650 cells. just wanted to know will it be safe if I connect 4 packs of 48v 200ah in series. As this pack will be used in ESS
Safety of your storage system depends on how the battery bank is installed and electrically connected, as well as the cable sizes, terminations, isolators and the safety devices used for protection
what about the BMS? Do we need the master BMS as we are worried about the unbalancing of the battery. and regarding the connectors , we will be using the proper connectors and terminals. as there was an article in which i read that for high rating 18650 li-ion battery pack can be dangerous….
That’s your choice as master/slave battery management systems add additional cost and complexity to a battery bank configuration. Please ask your second question to the writer of the article to which you refer.
I have 2 batteries 1 is 12v / 180AH (Liquid) and 2nd is 2v / 300AH (Dry) can I connect both in series for increase Amp and voltage must be 12?
Connecting your two batteries together in “series” will produce 14 volts at 180AH capacity.
Can I connect 35ah battery to a 100ah battery and can I connect maybe 6 35ah battery to 2 100ah battery’s in a battery bank
You can charge parallel connected batteries using a single charger but the battery combination will only charge upto the minimum Ah capacity, 35Ah in your case. This is because as the lower Ah battery reaches its fully-charged state, its terminal voltage rises which the charger detects and thinks the whole battery combination is fully-charged. The result is that the larger Ah battery never gets fully charged only to an amount determined by the lower battery. Thus it is not recommended to mix and match different voltage or a different amp hour capacity (or both) batteries within the same battery bank. Different Ah batteries will need to be disconnected and charged individually.
If I’m using the 24v series/parallel setup (connecting 2 sets of 6v battery banks) can these be hooked to a buss bar along with the controller and inverter. Presently I have this set up for 1 battery bank ( seems to work great) and want to add another set of batteries.
Yes why not?, as long as your busbar can handle the additional loading.
Sorry, I missed some details….They are 12 V batteries and I would run them 48V or 60V. needing 240V at cabin.