I’ve had a few instances recently where existing off-grid systems using Pylontech batteries have needed to be upgraded, and I haven’t been able to source the same model.
For example, a system with US2000 series batteries and a second system with US3000C batteries. The US2000 series is no longer available, and the only US3000 battery I could source was the US3000B (which seems strange).
I was able to find some compatibility guidelines in the Pylontech US5000 manual.
When there are US3000C and US3000B in the system, you must use US3000C as the master battery. In addition, since US3000B only supports up to 8 in parallel, when the number of batteries is more than 8, US3000B (and the same for US2000B) should be set in the 2-8th position.
I have found that Pylontech batteries are generally shipped at around 60% SOC, so you should always add new batteries when the existing batteries are close to 60%. This will enable all batteries to charge equally and balance out during the first charge. However, the new batteries sometimes have SOC, anywhere from around 45 to 65%. I just found this problem addressed in the manual - It states that “During capacity expansion or replacement, when parallel different 5.9Power offSOC/voltage of module together, it is recommended to maintain the system in idle for ≥15mins or till the SOC LEDs becomes similar…” So essentially the batteries slowly balance out once they are active. Still, they should be as close as possible when upgrading.