[wingtipper]

ok i did discharge and cycle the battery a few times . the difference is getting smaller , its now 0.10 volt down at full charge . also after 5 minutes in the plane on a static test , the 3 cells were 3.82 3.84 and 3.85 . so my guess is it is a borderline cell, however it lasted the time . also discharged on the charger at the same rate as another battery . so it might be ok .

That is encouraging. It could be that this cell has a slightly higher internal resistance than the other two cells, and so fell deeply out of balance since the initial conditioning charge post-manufacture. The good news is that this is not a necessarily a terminal (no pun intended) problem; the less good news is this cell will likely always be the runt in the pack.

You could confirm this somewhat by repeating the static test with a cell checker attached - a cell with higher internal resistance will show a larger voltage drop from its starting voltage while under the same load (although it is more reflective when the cells all start at the same state of charge, which may not yet be the case with your pack).

If this is the case, that cell will likely get slightly warmer than the other two under load, further accelerating its premature aging. If it's not the centre cell in your 3S, and if the battery placement in the airframe gives you the option, consider marking the battery so that the weak cell is not face-down/velcroed etc (i.e. keep it exposed if possible) to give it the best chance at living as long as its neighbours.

claudio , i'd like to give you advice on the drill . it's a dodgy thing to do , seeing that so may scenarios can eventuate , worst case being a sliced tendon .

No, would definitely have the prop well secured, regardless of how it is reamed (no desire to have my drill start generating thrust! ).

Was just wondering whether there is a trick I don't know to accurately drill concentric holes without a drill press, core drill bits, etc.

regarding the battery pack that sounds like the most likely situation Claudio . thanks . i guess i'll look at it as a 95% battery with a shortened life .