RE: why a ballancer
Chargeing lipo cells in series (even at a very slow rate) will cause any cell that's already full to go overcharged while the remaining cells are being brought up to full. The overcharge that a Nickel battery can dissepate as heat doesn't happen in a lipo. It continues to increase cell pressure and makes the cell start blowing up like balloon.
Nice thng about lipos is that if they are matched in capacity and used half way conservatively they will also stay in perfect balance for long time.