Yes. The battery can be put in parallel or series by customers. But there are few tips we need to pay attention

1> pls Make sure the voltage of each battery are same before put in parallel. If they are not the same, charge them to the same rate.

2> Don't not put discharged battery and  un-discharged battery in parallel. This may reduce the capacity of the whole battery pack.

3> Advise us the target capacity of the whole battery pack if you would like to put them in series. We  will choose the suitable BMS for each battery. 

4> If you are not professional connecting in parallel and series batteries, please don't handle the battery by yourself.

It may cause danger and shorten the circle life of battery pack.