Hello to all.
I want a BMS protection for a 3S 12V 18650 battery system with 18 Ah. But, I want to build two sets and plug them in paralell, including the two BMS. Can I do this? Best. António
Hi @Antonio, welcome to the forum 
Directly connecting lithium batteries in parallel is possible, but should only be done if they are at the same voltage, and with similar levels of wear (so that they discharge at the same rate). That’s very hard to guarantee, so for safety reasons it generally makes sense to use some form of switching circuit (like those discussed in this thread).