I have 2* 2S lipos 4000 mah batteries mounted in series which I use in my bruhssless E-Revo (hobbywing EZrun 2200 Kv).

I'm considering upgrading to 5s, and my local dealer sells 3s batteries (same brand) but with capacity of 4200 mah.

I've read the posts, and it seems that capacity must be the same for both batteries used in series.

Could someone let me know what would be the consequences of using one 2S 4000 mah together with one 3S 4200 mah? May I do that?

Many thanks for your answers already!