I'm using Molicell P26A batteries (and the TM 1.5) and when I charge they generally take just under 1600 Milliamps (of a nominal capacity of 2600). So in theory I still have 1,000 Milliamps left or roughly 40% of capacity. While the TM will shut down long before you reach 0 capacity, I'm definitely leaving some capacity on the table, so to speak. I'm not sure what is optimal in terms of how far to run them down, but I do charge them at a fairly gentle (and slow) 500 Milliamps.Do you have like 1/4 of the battery after that session? Not sure when to start charging for optimal battery longevity. I usually charge when it switch to blue or purple light, as the vapor produced on the same temp dial is reduced. Probably not the best way to handle batteries and device.
I'm generally sneaking away to take a toke, however, so the device running out of juice is a bigger monkey wrench for me than it might be for others. As a result I prioritize not running out of power mid-session over using all of the capacity, even if that isn't best for the battery (because it is best for how I use the device on a practical level). And I suspect it does not make a dramatic difference to battery longevity.