Peter_DM

I think @Nexuss may have hit the nail on the head here saying that different programs present the data differently
Another switch I made recently was away from ICC and the various Inverter Apps to Home Assistant, so that may be a reason I didn't spot this phenomenon until now
Thank you all for the info, I accept that this is normal behaviour for the Pylontechs
It's really fantastic to have this level of knowledge & support available

Ah! I should have twigged to that from the 220 V (not 90 V as is more commonly seen) between neutral out and earth.
It's one of those errors that someone like myself can't conceive of making. I'm not saying I would never make that mistake, though I sure hope not, just that I'd never think to check for it.
Great to hear that it's sorted.

I'm not sure why Chris posted his question here - I'm thinking he's suggesting that for me.
To answer your question about my setup, I have 2 x Axpert 5KVA Inverters for the main house, each Inverter has 12 x Canadian Solar 255W panels (in 3 strings of 4). The battery bank for these Inverters is 32 x 105AHr Dixon Lead Acid Batteries (in 8 strings of 4).
Then I have a separate 5KVA Axpert for my cottages, and that has 9 x newer Canadian Solar 335W panels (in 3 strings of 3). The battery bank for this Inverter is 3 x PylonTech US3000 Batteries.
Each of the above has a Pi ICC monitor, and I've now ordered the Victron 702 for the house Inverters.
I don't have any MPPT's, relying on the Axpert internal units.

The batteries that I'm talking about are just over 2 years old.
I do have 3 x Pylontech US3000's (recent purchase) for my secondary inverter, I've split the property into main house / cottages.
Any future batteries I buy would be LiIon (or better - been hearing whispers about super cap batteries lately); in the meantime I will try to look after these lead acid batteries as best I can, till I have to bury them 😉
Thanks all for the input / feedback / information

Now with all that info about parallel strings, read this paper. Through careful management you should be able to get 80% or so of the normal life out of them, but the important part is you have to actually cycle them do a decent depth (ie no shallow cycling), and you have to err on the side of overcharging (cause undercharging kills the weaker cells faster than overcharging kills the stronger ones, especially if they are flooded).
What will happen then, is one day you will notice that some of your batteries are showing lower voltage or boiling away more water, and you will then test them, throw them away, and reduce your 8 strings to 7, and then to 6... and eventually you'll go LFP 🙂 But in the mean time... enjoy them and look after them as well as you can. That is my opinion.

The documentation explains how you can link the midpoints through a fused connection so you can monitor them all at the same time. But I have to admit, the idea of linking 8 strings in that manner is a bit more than the usual 2 or 3.
The problem is mostly during charging (to a much lesser extent on discharge), so I will just focus on that. Electricity takes the shortest path, and 8 strings means there are 8 possible paths to go. As current passes through a battery it causes a chemical reaction which recharges the battery. No two batteries/cells are exactly the same and they don't respond similarly to changes in temperature either, so the current you push through there never divides equally into 8. Some batteries therefore charge faster than others. Once a lead acid battery is full it will continue to accept charge, but all the energy you put into it essentially just turns into heat and/or boils away electrolyte (so flooded cells where you can replenish the water handles this better). But because of the disproportionate absorption, you can't stop charging when the first cell(s) are full, you have to continue until all of them are, which means that the only way to get the slower ones fully charged is to overcharge the faster ones. This is made worse because better/healthier batteries naturally accepts charge easier, while older/weaker ones naturally accepts charge a bit slower. The result is that the best batteries are damaged through overcharging, and the weakest batteries are damaged through undercharging.
The more batteries you have, the higher the odds of things going bad. In addition to that, there is a bit of an inverse correlation between battery size, popularity and quality. The 100Ah is a popular size for UPSes and are made in large numbers/bulk with less attention to quality. 200Ah batteries are less popular, not used so much in smaller UPSes, bought by a different kind of customer, and tends to be less... well... crap.
So 4 strings of 200Ah btteries is better than 8 strings of 100Ah even though technically it's the same capacity.
Which brings us to Dixon. For the most part, a good battery, especially the golf cart 6V units. I have however decided I will rather fit Sabatt to my cars in the future... in my experiene Dixon car batteries are rubbish, so much so that I'd rather go with another cheap make 🙂

So I'll be looking for a Nitrogen supplier? 😊

Googling it seems to say a dehumidifier has a greater capacity to dehumidify than an air-con and reading between the lines it would seem cheaper to run as well.

Whether the terminals point up or to the side... the battery cells will be on their side. and is allowed.