[jacquesm]

> please ensure you first educate yourself about thermal runaway

YES!.

That's why you should monitor a setup like this with a FLIR from all sides during the first month of operation or so, if no batteries ever run hot during charge/discharge cycle you may be good to go. But better keep an eye on that balance, especially in packs that are sitting at high voltage for a long time (like this one does) because you won't know how the pack behaves during discharge and recharge and that is likely when any problems will be most apparent.

Thermal runaway can happen very quickly once a certain threshold has been passed.

If you really want to do a project like this with Lithium Ion and you are not space constrained you would do better to have a bit less capacity and charge the batteries to 3.6 ... 3.8V or so. That would work much better in the long run.