Is it possible to use a 6s battery and a 4s battery to configure a 10s battery? I can’t see why it shouldn’t work as long as the capacity is the same. Am I missing something?
yes it would work assuming that the cell specifications are the same
this is how your series wiring would work
red circle = Positive orange rect = negative black rect = cell black line = conductive material/link/wire etc
1 Like
Perfect! Thank you, that was what I was thinking too 
Yes, but you should aim for the same brand, model, discharge rate, capacity, ect. When connecting in series, you want them to discharge at the same rate, so you don’t over discharge any cells. I’m splitting the 18650 battery pack I’m making now into a 7s4p and a 3s4p. Essentially, I’m just connecting the two packs in series.
Yes @evoheyax is exactly right but I want to also add that you want the cells to “age” together. Meaning don’t combine a new pack with an old pack. They need to roughly be used the same amount and “age” as one battery
1 Like
That’s true. I forgot to mention age. but age matters less if you have a big battery pack 
The concern with age is, as a battery ages, it holds less of a charge. It may seem like they have the same voltage when fully charged, but it will discharge quicker than the newer pack, and your susceptible to over discharging the older one this way. It’s less on an issue with 18650s, much ore of a problem with lipos due to their short life.
2 Likes