# Interest group forums > Energy and Resource Conservation Forum > [Question] Which 48 volt lithium battery is the best

## Isetech

This seems to be a more difficult task than I could have imagined.

What do you consider when choosing a backup battery for your inverter or solar system? 

1/ The type of cells used? 

2/ The type of BMS used?

3/ Temperature monitoring? 

3/ How the battery temperature is managed during charge and discharge cycles? 

4/ Compatibility with the inverter you choose. 

5/ Charge and discharge rate, this seems to be trick question, normal, max or advisable 

6/  Life cycles? how many time it can be charged and discharged 

7/  Designed life expectancy, 10 or 20 years? 

8/ Firmware and software compatibility with inverters?

9/ Type of BMS of communication? 

10/ parallel connections, how many etc? 

Those days of talking about a the thickness of the lead cells or the battery case base and battery amperage only is a thing of the past. 

Batteries have become complex little power houses.

what I thought would be a simple question, who makes the best bang for your buck with all the frills. 

Which battery is the best and why? Can anyone supply credible data comparing lithium batteries with lithium batteries.

I bought a blue nova battery and cut it up to see what it looks like inside. It was assembled better than I expected. 

Maybe I should buy each battery sold in SA and strip it,  check things like the QR on the cells to verify the information on the data sheet, do capacity checks and show everyone how they are built.

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## Isetech

I do realise my warranty would no longer be valid  :Wink:  I am not sure that there would be any legal implications, I see guys doing it on youtube all the time.

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## Isetech

Lets start with the cells.

BYD prismatic cells seem to be the preferred ones. They advertise -

*The cell has a larger surface area than regular prismatic cells, allowing for better heat dissipation. The cells also allow for slow heat release, lower heat generation, high starting temperature for exothermic reactions, and do not release oxygen during thermal runaway.

*
It looks like I will be spending the next few weeks doing research into lithium batteries.

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## Isetech

I still cant find someone to answer what I thought would be a very simple question, how to determine the C rating of a battery in manner which can be used to compare information published on data sheets.

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## Justloadit

BU-402: What Is C-rate?

The C is usually provided by the battery manufacturer.

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## Isetech

The protective device controls the C rate? 

If one battery has the same capacity and cell type, then the manufacturer would control the charge and discharge rate protection? 

Buying a 0.5C or 1C battery cycle life would perform the same and the life cycle would be the same if both charged and discharged at the same rate at the same temperature?

The 0.5C would have internal protection to prevent the battery being "hammered" with high charge and discharge rates, hence a higher life cycle advertised? 

A 1C battery protection would be toned down, allowing the battery to be "hammered" thus reducing the life cycle? 

All just question it seems impossible to find out from any of the suppliers. I have tried contacting numerous outlets and manufacturers, either "we are experiencing high call volumes please be patient" or I have left messages and nobody returns my calls. It seems the call centre are manned by operators with a spec sheet with just enough info to answer most common questions, most of us know already. 

I will just keep scratching until I understand. 


"While lead- and nickel-based batteries can be discharged at a high rate, the protection circuit prevents the Li-ion Energy Cell from discharging above 1C. The Power Cell with nickel, manganese and/or phosphate active material can tolerate discharge rates of up to 10C and the current threshold is set higher accordingly."

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## Isetech

I think its time to buy a few different batteries and open them, check if they have QR codes on the cells, then see how they are assembled.

I have already popped open a blue nova battery ( yip warranty out the window),  I am going to have to cut the plastic off, then get a blow torch to remove the resin. 

Any legal experts know if it will be ok for me to post pics of the battery in pieces? I see the youtubers do it all the time, so I am assuming there will be no issues?

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## Isetech

Could the C rating be reduced to protect "seconds" (not off the production line) batteries?

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## Isetech

https://www.power-sonic.com/wp-conte...y-C-rating.pdf

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## Isetech

I see it is official, you get a 10 year warranty for your Sunsynk setup if you use the Sunsynk battery with the Sunsynk inverter, why would you you sacrifice a 10 year warranty and use any other battery?

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## Isetech

When selecting the battery for your system, how would the C rating affect the design? 

From the little experience I have installing inverters, you never want your system to be pulling 100% @100 amps if you are using a 100 amp/hr battery, especially if you are using the system as a backup (UPS type). You would need a pile of batteries if that is the case, then 0.5 or 1 C wouldnt be a a priority.

An example: If you are using it for critical/essential loads, which generally the case in SA, the system should not not be fully loaded at any point, you want the system to support your essential loads at any point of the day or night with at least 6 hours of support, preferably longer, but they budget would determine the support period. The longest life cycle would be the better option, not the higher C rating. 

Another example would be a small workshop. A battery which can handle the full discharge capacity for short bursts would be a good option, because you might be running small machine with motors which start up. You are looking for a system to keep the workshop flow. 

It all seems to keep going back to one thing, design for the application. The solar and inverter audits fails seem to point at bad design. Understanding and designing the system around the customers application seems to be the missing link.

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## Justloadit

> Could the C rating be reduced to protect "seconds" (not off the production line) batteries?


The BMS in the batteries, only provide 2 functions as far as I know.
1 - If the battery voltage drops below a predefined value, it disconnects the battery from the load. Gets enabled when the charger is enabled
2 - In the case of a short circuit, then the BMS will disconnect the battery from the load. I am not sure here but i think it is again enabled when the charger is enabled.

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## Justloadit

> When selecting the battery for your system, how would the C rating affect the design? 
> 
> From the little experience I have installing inverters, you never want your system to be pulling 100% @100 amps if you are using a 100 amp/hr battery, especially if you are using the system as a backup (UPS type). You would need a pile of batteries if that is the case, then 0.5 or 1 C wouldnt be a a priority.
> 
> An example: If you are using it for critical/essential loads, which generally the case in SA, the system should not not be fully loaded at any point, you want the system to support your essential loads at any point of the day or night with at least 6 hours of support, preferably longer, but they budget would determine the support period. The longest life cycle would be the better option, not the higher C rating. 
> 
> Another example would be a small workshop. A battery which can handle the full discharge capacity for short bursts would be a good option, because you might be running small machine with motors which start up. You are looking for a system to keep the workshop flow. 
> 
> It all seems to keep going back to one thing, design for the application. The solar and inverter audits fails seem to point at bad design. Understanding and designing the system around the customers application seems to be the missing link.


Agreed, full C in my opinion should be reserved for instantaneous requirement of any load for a short period of time.
I usually like to cater for at least 6 hours of load on my battery pack, preferably 10 hours. 
At 10 ours it ensures longer battery life due to the reduced period of charge time at a high rate to bring the capacity up to cater for the constant load shedding experienced in recent days.

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## Isetech

I see Sunsynk have 2 types of batteries 


CATL Battery SSLB1

BYD Battery

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