Delong Battery Pack Varied SOC

[PG_SEB_NZ]

I live in New Zealand and have purchased three 10kWh LiFePo battery packs (total 30kWh, 3 x DL-LFP-51200's) from Delong Battery Technology (DelongTop) from Shenzhen, China. I have been having a problem with the three packs getting progressively further apart regarding their individual SOC % (State of Charge). It got serious a month ago when we had several days of wet weather, and two of the packs were showing about 45% SOC while one pack was only showing about 25% SOC.
I noticed that when the packs were being charged their BMS sent the highest SOC value of the 3 packs to the Growatt Inverter/Charger, (displayed on the inverter screen), but when they were discharging the BMS sent the lowest SOC value. This meant that I was not going to be able to use the extra storage that was in the two higher SOC packs when the inverter inevitably shutdown due to the minimum SOC alarm setpoint being reached, (set to 20% SOC).
It is impossible to get any sensible answers from the Delong Support people because none of the engineers speak English. Has anyone else encountered this SOC difference problem from the Delong battery packs before? I am also keen to find out how many of these new Delong 10kWh pack have been sold into NZ and Australia.

[gfwilliams]

Hi - did you have any success with this in the end?

I've got 10x Delong 2.5kWh rack mount batteries that this started happening to after about 18 months, but when I started looking into it I found that 1 or 2 of the cells in each pack had gone 'high resistance' meaning that the other cells in the pack couldn't be charged. I've been on to Delong support as the batteries should have had a 10 year warranty (and they managed 18 months and 300 cycles!) but they are refusing the honour any kind of warranty on them.

I asked on DIYsolarForum about them, and the consensus seems to be that the BMS was set up wrong from the factory so that cell balancing wasn't happening until the cells were at such a high voltage they risked damage... You may be able to use the software they posted there and adjust your packs (and lower charge voltage) and hopefully it's not too late... But in my case the batteries are now effectively trash, with several of the rackmount cases visibly bulging.

So all I can suggest to anyone else reading this is to avoid buying from Delong/Delongtop - the 'warranty' isn't worth the paper it's written on and when they are in China there's nothing you can do about it.

If you do have Deiong packs, ignore their documentation which states you should charge at 58.4v, and make sure you lower it significantly - at least that should reduce the likelihood that cells get over-volted and destroyed.