9 hours ago, Bobster. said:

I'm confused by the data being shared here. To be clear I'm not disputing any of it, I just don't understand.

Is it the case that we get more cycles from a LiPo battery if it gets discharged past 50% remaining SOC on a regular basis?

If you are referring to the two graphs and table that I poster, then no! Both the graphs show that the deeper the depth of discharge (DOD) is, the less the ultimate life of the batteries are. What might be confusing is the concept of Depth of Discharge - this is the opposite from what we usually use, State of Charge (SOC). 100% SOC ~ 0% DOD, and 10% SOC ~ 90% DOD, etc. As an example, using the first graph, if you discharged only 20% of the capacity (20% DOD or 80% SOC) one could expect to achieve just less than 30 000 charge/discharge cycles, whilst at 80% DOD/20% SOC one would only expect a bit less than 5000 cycles.

The number of cycles seem very high to me, but it is a heavy duty transport type battery used in busses, thus nor really appropriate to our use, although the principle remains the same. The table from Battery University that I posted is probably simpler to understand, but keep in mind that they compare the life of NMC batteries with those of LiFePO4. In that table, they quote the expected life of a LiFePO4 battery to be about 600 charge/discharge cycles at 100% DOD/0% SOC, compared with some 9000 cycles if only discharged 20% (thus 80% SOC remaining).

3 hours ago, Bobster. said:

With my inverter it is difficult to stop the battery charging to 100% unless the weather is pretty miserable. It maybe easier with Deye/Sunsynk. Can you control the MAXIMUM SOC with those?

I think that is the crux for us home PV users - My Sunsynk system also cannot charge to only 80% or 90% when using solar, and I'm not aware of any home-use system that can be set to charge to only a % of the total battery capacity - I anyone can point us to such a system then please do...

I did query this exact problem with the Sunsynk help desk a while ago, and insisted that they open a ticket requesting such a feature to be added in a future upgrade, if possible. One of their senior technical people responded by email the next day and stated that their batteries won't be degraded by the short 100% SOC daily charge, given that this condition only lasts for a few minutes (I timed about 10 minutes) before the SOC drops to 99% whilst the PV supplies the house load. So, I have it in writing from them that they guarantee the 6000 cycles even when charged to 100% every day (obviously only at 25 degrees C battery temperature - read the small print 😁)

Apologies to @Carel.Rossouw for hijacking his thread.

3 hours ago, Bobster. said:

Thanks.

With my inverter it is difficult to stop the battery charging to 100% unless the weather is pretty miserable. It maybe easier with Deye/Sunsynk. Can you control the MAXIMUM SOC with those?

Also I note that there's talk of about 500 cycles. My 10/8 is warranted for 6000. And they're comparing cell phone batteries (I think) with EV batteries. I think the sort of battery we use in domestic installations is closer to an EV battery.

My MUST inverter allows me to set what SOC to charge to. This is my first inverter so I’m not too sure how others can be configured.

As far as I know, Lipo and Lion is basically the same chemistry. The real big difference is that Lion is liquid electrolyte whereas Lipo is a more solid gel like electrolyte. Kinda like Flooded LA Vs AGM/GEL.

The same recommendations for not charging to 100% apply to Lipo. The 500 cycles they mentioned for cellphones I believe is because they are assuming an individual would charge from 0 to 100 and rinse and repeat, No heat management (I’m sure we all have felt our phones getting hot when charging) which contributes to the 500.

Do you have the datasheets for the batteries you have? The 6000 cycles is typically at 0.2C discharge, a specific temp and I assume 80% DOD? In real world applications it may be about 3000 as lots of people excede the 0.2C rating, batteries are not idle at the specific controlled temp the manufacturer has it at etc.

Edited August 6, 20251 yr by Denns

5 minutes ago, HennieL said:

If you are referring to the two graphs and table that I poster, then no! Both the graphs show that the deeper the depth of discharge (DOD) is, the less the ultimate life of the batteries are. What might be confusing is the concept of Depth of Discharge - this is the opposite from what we usually use, State of Charge (SOC). 100% SOC ~ 0% DOD, and 10% SOC ~ 90% DOD, etc. As an example, using the first graph, if you discharged only 20% of the capacity (20% DOD or 80% SOC) one could expect to achieve just less than 30 000 charge/discharge cycles, whilst at 80% DOD/20% SOC one would only expect a bit less than 5000 cycles.

The number of cycles seem very high to me, but it is a heavy duty transport type battery used in busses, thus nor really appropriate to our use, although the principle remains the same. The table from Battery University that I posted is probably simpler to understand, but keep in mind that they compare the life of NMC batteries with those of LiFePO4. In that table, they quote the expected life of a LiFePO4 battery to be about 600 charge/discharge cycles at 100% DOD/0% SOC, compared with some 9000 cycles if only discharged 20% (thus 80% SOC remaining).

I think that is the crux for us home PV users - My Sunsynk system also cannot charge to only 80% or 90% when using solar, and I'm not aware of any home-use system that can be set to charge to only a % of the total battery capacity - I anyone can point us to such a system then please do...

I did query this exact problem with the Sunsynk help desk a while ago, and insisted that they open a ticket requesting such a feature to be added in a future upgrade, if possible. One of their senior technical people responded by email the next day and stated that their batteries won't be degraded by the short 100% SOC daily charge, given that this condition only lasts for a few minutes (I timed about 10 minutes) before the SOC drops to 99% whilst the PV supplies the house load. So, I have it in writing from them that they guarantee the 6000 cycles even when charged to 100% every day (obviously only at 25 degrees C battery temperature - read the small print 😁)

Apologies to @Carel.Rossouw for hijacking his thread.

It is fine I’m also learning something new.

34 minutes ago, Denns said:

My MUST inverter allows me to set what SOC to charge to. This is my first inverter so I’m not too sure how others can be configured.

As far as I know, Lipo and Lion is basically the same chemistry. The real big difference is that Lion is liquid electrolyte whereas Lipo is a more solid gel like electrolyte. Kinda like Flooded LA Vs AGM/GEL.

The same recommendations for not charging to 100% apply to Lipo. The 500 cycles they mentioned for cellphones I believe is because they are assuming an individual would charge from 0 to 100 and rinse and repeat, No heat management (I’m sure we all have felt our phones getting hot when charging) which contributes to the 500.

Do you have the datasheets for the batteries you have? The 6000 cycles is typically at 0.2C discharge, a specific temp and I assume 80% DOD? In real world applications it may be about 3000 as lots of people excede the 0.2C rating, batteries are not idle at the specific controlled temp the manufacturer has it at etc.

This has been discussed on power forum before. The reality is that all guarantees from battery manufacturers are qualified (which may be reasonable), and the quoted life figure has lots of asterices & small print.

I mentioned the 6000 cycles here because it's so different from what was mentioned in the linked documents, and so I conclude that it's a different kind of battery.

Mine is advertised at 6000 but I haven't read the data sheet. The performance has been entirely satisfactory.

9 hours ago, Bobster. said:

This has been discussed on power forum before. The reality is that all guarantees from battery manufacturers are qualified (which may be reasonable), and the quoted life figure has lots of asterices & small print.

I mentioned the 6000 cycles here because it's so different from what was mentioned in the linked documents, and so I conclude that it's a different kind of battery.

Mine is advertised at 6000 but I haven't read the data sheet. The performance has been entirely satisfactory.

I have been taken back by the fact that a user has already taken his out of the battery bank after only 4 years. Having 30% capacity left in 4 years is a far cry from 4000 plus cycles with 80% DOD.

9 hours ago, Bobster. said:

I mentioned the 6000 cycles here because it's so different from what was mentioned in the linked documents, and so I conclude that it's a different kind of battery.

I wondered about that myself, and came to the conclusion that it's due to a difference in the definition of "end of life". The guaranteed by Sunsynk is actually that the battery will retain 60% of it's new capacity after 10 years, with a maximum yearly cycle count of 700 charge/discharge cycles (thus less than 2 cycles per day...). The graphs posted previously presumably count the number of cycles until the battery cannot hold any charge, hence the much higher cycle count...

5 minutes ago, Denns said:

I have been taken back by the fact that a user has already taken his out of the battery bank after only 4 years. Having 30% capacity left in 4 years is a far cry from 4000 plus cycles with 80% DOD.

Agreed. As you mentioned in an earlier post, the "life is also related to charge/discharge current (0.2C being a test condition for Sunsynk), and even more importantly, by the temperature at which it is charged and discharged. We tend to keep our batteries in a garage or other outbuilding, of in a small closet, or even bolted to the outside of the house, which in South Africa equates to a temperature variation from below zero to over 40 degrees C, depending on where you live. If enclosed in a small space, or with a hot car engine parked right next to it, or exposed to direct sunlight, the battery could easily reach (say) 60C or even 70C, and that would be very bad for battery life. On the other hand, charging the battery when it is below 0C is even worse...