Beat

I personally don't like the idea of one big battery and prefer several smaller ones. If one fails it can be taken care of while I'm still in business with the other ones.

Because they don't want you to buy from competitors.

It is save to mix battery packs with the same chemistry and the same number of cells. The size (Ah or kWh) may be different, no problem. The compatibility of the BMS is another story. However it looks like most BMS support RS485 protocol for pure monitoring.

Good for you! Not everybody is such a Hercules that can lift 70kg, neither am I.

On my 3 older LEOCH 48100TB the BMS calculates SOC by counting metered Ah in and out but neglect the internal losses. The result is their SOC readings are always to optimistic. When approaching full charge their BMS display 100% SOC while the batteries have not yet reached full charge voltage and continue charging. Therefor I prefer charge managing by the Inverter on the base of battery voltage without interference from the BMS via coms.

I have: Its a LEOCH 48100-S. I have no coms and use inverter settings for bulk and float charge voltages according to specs of the battery manufacturer. According their recommendations the bulk charge remains for 1 hour to allow for balancing. However it looks like it has no effect. Averge refuses a guaranty claim by arguing that the pack still has full capacity according to specs.

I think you don't need an additional MPPT. Connect the west roof panels in parallel with the east roof panels. This will not overload the MPPT since the east and the west panels will never deliver full power at the same time. I have such a situation and write from experience. Condition is however that east and west panels are of the same type (same number of cells).

This statement being classified "bad advise" any further discussion becomes obsolete. I stop it right here.

Think about handling, i.e in case of requirement to move them. A 4.8kWh battery weights about 45kg. 2 persons can handle this but everything larger would require lifting devices. Better make up your storage needs with several handy units. Also in case of failure of one it would impact the system less.

That's what I thought too. But on my bank of 6 packs I observe the following: During charge and discharge all packs show quit coherent voltages with the inverter, taking measuring inaccuracy and voltage drop in the cables in account. However at full charge with no current some of the packs voltage deviate from others and from the inverter up to 1V. I have no explanation for this other than weird BMS. What I don't know and wonder is whether the terminal voltage readings are measured at the terminals or just the mathematically adding up of the cell voltages.

Tinbum, you are a genius for imagination of extreme scenarios, that 99.99% of users never experience. This forum as well as the inverter forum are full of threads complaining about BMS to inverter comms issues. The actual thread is a typical example. The author neglected proper inverter settings assuming the BMS would take care of it. But that didn't happen. I cannot remember any thread with an issue caused by the lack of such comms. I conclude that comms cause more issues than they resolve. One cannot over emphasize the importance of proper inverter settings according to battery specs, with or without comms. Just figure out if there is or is not a risk.

Quit a horror scenario you fantasy. My solar panels can never deliver so much power that could overheat the batteries with charging. The total nominal 6kW never deliver at the same time thanks to different orientation. The grid charging current is limited to 0.1 C of the batteries. Besides, if one had so many panels to present a risk, he could limit the charging current in the inverter settings.

What you mention are protective parameters, not charge managing. If any those exceeds critical value by internal cause the BMS has the ability to disconnect itself from the terminals. If you have a bank of several battery packs there is no need to intervene with the inverter leaving the rest of the system functional. What you need however is periodically monitoring of the packs. I do it with a RS485 bus connected to each pack and wired to a laptop in my office. You might also do it with WiFi.

I strongly disagree with you. From my experience with BMS weird behavior I get goose bums thinking those could control the inverter. Inverters are designed to manage charging on the base of battery voltage. That information never lies.

Reading trough this tread resurfaces my old question: What can BMS comms do better than proper inverter settings? My inverter settings with no comms according to battery specs for 15 cells are: Bulk charge 53V held for 1 hour, float charge 51.5V. These values have never been exceeded. With these settings healthy battery cells never go into OV state.