There is no need to use a heatsink at ambient temps in the 60's. All you are doing is supercooling your cells, causing them to lose power. I won't even think about using mine until the ambient temp is in the 80's.
I suppose that using the heatsink when in lower temps could potentially cause the batts to last longer, but IB4200 cells seem durable enough already to withstand being lukewarm
. You just don't want the IB cells to be over
heated during charge.
Battery temps should be reaching the 45-50 deg C range as they peak on the charger. Check out our article here:
Summary of MMR Charging Accessories
mAH readings during charge can be deceiving with IB cells. I had old 3300's that could take 4400 during charge. IB cells seem to almost charge quicker as a general rule...their lower resistance may be what is contributing to their high run-time compared to previous cells. Also, we do not equalize IB's as low as we did GP's. It was actually common for some batches of good 3800's to only take 3700 during charge, even if they were equalized to .6 beforehand.
Don't place too much emphasis on the amount of mAH the batteries take during charge. It is just not a consistent reference. The big thing is that the batteries both get a full charge and get up to temperature.
It was doubtful those 3300's I had (that took 4400mAH) would make full run-time in mod. My old 4200's (that take only 4300mAH or so), however, sometimes have over a minute left after a mod race.
5A equalizing before charging can effectively make your pack take more mAH during charge...it can make a difference of up to 400mAH with 4200's in my experience.