oh dear god.. he spreads his wings........
This has been debated to death on ES, countless warnings, and safety concerns expressed...
Can used laptop cells be used for an ebike ? Yes
Is it a good idea? .. NO>
For the 1% of the population who will be willing, able, and determined enough to deal with the risks, it can be done.. but the rest of the world should not follow the advice above... there are way too many details missing, and far too little warnings.
For starters. 4.1v vs 4.2v is not accurate enough... and saying that the first several charge cycles were monitored is also not sufficient info.
I personally have multiple high powered ebikes, running on RC lipo, i bulk charge them all, and none of them use a BMS... I am part of that 1% group.
Before, and After, EVERY cycle, i check cell voltages with a cellog, i always remain present during charging ( not sitting staring at the pack, but am within range at all times, and i NEVER go to bed while a pack is charging ) .. I set my bulk charger to get an average cell voltage from 4.15~4.18v, without balancing, but if at any point, a single cell/group goes outside this range i hook up the RC charger to that cell/group and bring it back into proper range, if it remains in check for another dozen or so cycles i keep doing this.. but if after 1 or 2 cycles that cell/group drops out of range again, i open the pack and repair it.
When i ride, all my bikes have Cycle Analyst meters, so i monitor Amp/Hour used very closely and never exceed 75% of my known available capacity.
If any of the above seems like too much work or bother... you belong to the 99% group and should not copy the efforts above.
ps: SLA is not wasting power as Heat ( entirely... ) , it's a reaction called Peukert Effect :
http://en.wikipedia.org/wiki/Peukert's_law