Chris Scott:
Probably 7 cellīs in series. Why?
A LiIon cell typical max charged voltage (4,2 v ea.) for 7 cells means 29,4 V. Iīve heard of a Diode in the circuit (in series, dropping the voltage to ~ 28 V).
Nominal voltage of 25,9 V (7 x 3,7V). Less the Diode drop means ~ 24 V.
Subject to confirm it. Anyway, 6 cells is not enough and 8 is excessive.
(May be multiples of 7 if series parallel config. was used, with
higher risks) Will comment on that in a subsequent post.
(8 cell arrangement could be used if the circuitry is designed for).
I would design with 7 cell. Quite compatible with aircraft traditional batt. Voltage.