Laurence I have no idea what DS821's are but my guess is you are using a 2.4 system and for that reason and the size airplane I remember from your previous postings I would indeed use a six volt pack (five cell) and not a 4.8. I refuse to use 4.8 in any of my airplanes except just a couple of controlline airplanes that I use 2.4 for throttle.

I have never had a brownoout or low voltage problem ever and perhaps because of this and the fact I do not scrimp on the Mah's of my battery packs either. That include my early use of XPS 2.4 and now Hitec with some fifty receivers installed in an eclectic variety.

My recomendation is a five cell pack starting out at around 2000 mah

John