As far as I understand, SOH is a measure of how worn out your battery is, ie the % of the installed capacity that the battery can still charge.
After 2.5 years, mine says it has lost 6 % ie SOH = 94 %.
This got me wondering :
a) is this normal ?
b) are there any charts of expected SOH over time ?
c) is using 'force charge' responsible for the decline ?
Wondering if this is a linear thing ie lose 10% installed capacity every 3 years, or if it declines at an increasing rate over time ? Trying to get an idea of how many years of life I've got left in the batteries before they no longer meet my needs ( installed capacity 16.5 kwh, need minimum 10 kwh, currently daily charged energy = 12.6 ).
My battery took a long time (just over a year) to loose 1%, then a few weeks later it lost 2% in a single night 
I am not sure of all the answers to your question, as I am not sure there is a chart, and rate of lost SoH will vary from one install to another, depending on factors.
From what I can read and understand from a post from Dave Foster a while back, it seems to have an Annual loss, and I think year one tends to be the greatest, and then settles down. The BMS will also tot-up the times when the battery is under stress (high/low Temp and spending too long at 100% SoC, maybe being at 10% for too long also buggers it up)
I am not sure of all the answers to your question, as I am not sure there is a chart, and rate of lost SoH will vary from one install to another, depending on factors.
From what I can read and understand from a post from Dave Foster a while back, it seems to have an Annual loss, and I think year one tends to be the greatest, and then settles down. The BMS will also tot-up the times when the battery is under stress (high/low Temp and spending too long at 100% SoC, maybe being at 10% for too long also buggers it up)
Thanks for the reply.
Curious about "spending too much time at 100% SoC".
Not a lot we can do about that when the sun's out and its too hot to put the oven on !
But it does mean that in winter, perhaps I need to rethink use of "force charge" -
I guess charging up to 100% every night in winter is not such a good idea ?
What maximum figure should we be looking at - 90 % ? 95 % ? - so as to strike a balance between
getting cheap overnight electricity and not knackering the battery ?
Curious about "spending too much time at 100% SoC".
Not a lot we can do about that when the sun's out and its too hot to put the oven on !
But it does mean that in winter, perhaps I need to rethink use of "force charge" -
I guess charging up to 100% every night in winter is not such a good idea ?
What maximum figure should we be looking at - 90 % ? 95 % ? - so as to strike a balance between
getting cheap overnight electricity and not knackering the battery ?
During Winter, charging to 100% is fine, and I don't bat an eyelid at it. There are some that will suggest 80% to 100% based upon websites posting information for the wrong cell types. I plan to use my battery, and I want to use the 10-100% full range, I am not worried about degradation that much, and I want to have that 90% on tap.
During Spring, when the PV is more impactful, then I have an automation in Home Assistant to dump power in the morning, just after the cheap rate finishes. It looks at the PV forecast and if it thinks there will be enough (I have it set to 12kW estimated production) then I have it dump the 100% SoC down to around 55% give or take. I do this to have the battery not sit at 100% SoC for too many hours, and it also has a second benefit of 'mopping' up the PV above my export limit.
Example, nice sunny day forecast, power is fed to grid. If the PV goes above my 3.9kW export limit, I can then mop this up with the room in my battery. Typically it creeps up to 75-80% SoC before the 4pm peak, and I have spare SoC running up to the off-peak (so I can choose to export the leftover if I want)
FYI: I have my default running mode set to 'Feed-in' mode, so that it doesn't keep trying to charge battery back to 100% with PV in 'Self-use' mode. This puts house load -> export -> battery as the distribution of power, the battery only charges when the export limit is breached, so you don't clip PV output.
During Spring, when the PV is more impactful, then I have an automation in Home Assistant to dump power in the morning, just after the cheap rate finishes. It looks at the PV forecast and if it thinks there will be enough (I have it set to 12kW estimated production) then I have it dump the 100% SoC down to around 55% give or take. I do this to have the battery not sit at 100% SoC for too many hours, and it also has a second benefit of 'mopping' up the PV above my export limit.
Example, nice sunny day forecast, power is fed to grid. If the PV goes above my 3.9kW export limit, I can then mop this up with the room in my battery. Typically it creeps up to 75-80% SoC before the 4pm peak, and I have spare SoC running up to the off-peak (so I can choose to export the leftover if I want)
FYI: I have my default running mode set to 'Feed-in' mode, so that it doesn't keep trying to charge battery back to 100% with PV in 'Self-use' mode. This puts house load -> export -> battery as the distribution of power, the battery only charges when the export limit is breached, so you don't clip PV output.