The first and third discussions were very useful. The second not so. Read on though
I had 8 x 12 volt lead-acid batteries connected in series to provide 24 volts. They are also charged using a MPPT inverter powered by 8 x 3000 watt PV panels. Worked ok, and I managed to exchange 2 of the batteries under warranty with Communica after a series of arguments with their management who I discovered bend over backwards not to honour warranties
In March I got two Blue Nova 24 volt Lithium-ion batteries and connected these in parallel. Within 3 weeks one battery was showing "COM failure" and measuring it, it discharged at a much greater rate than the other.
I then found the BN staff ill-informed as to what to do. The booklet that accompanies the batteries refers to a LAN connection to balance them. There was no LAN connection which I noticed when collecting them and I was told that this facility was disabled as it was unnecessary. The fellow who initially dealt with my complaint had no idea about this and talked about "load balancing" but did not know how to do it and asked me whether it was not described in the book (he had no idea). He insisted that there should be a LAN connection and carried on about it until I suggested he speak to his boss
After 10 days of messing about I sent a strongly-worded email to the CEO. His immediate response was to offer me a brand-new unit with double the capacity which would have cost R11500 extra, for R6000. It also has a 10-year warranty and I insisted on a written guarantee explanation
I let the new battery settle down for 10 days and tested it. With a 350 watt load at 230 volts (14 amps at 28 volts from the battery), it dropped from 99% state of charge to 60% state of charge in 14 hours.
To my mind this is amazing performance. It has been sunny in Cape Town these past 2 days and the battery reached 98% state of charge by 15h45 today. For the test I configured it to charge from PV panels only, not mains. But to enhance battery life I usually let it charge from the mains. The real purpose of the system is for load shedding, although there has been a welcome reduction in electricity charges
I am not that keen on batteries in series without a sophisticated charge controller, having had indifferent performance due to one battery in a set failing.
