siai47 and Aerowhatt, I am in complete agreement that cell balancing should be performed periodically.
There are three techniques for cell balancing:
* Top balance (like the i-MiEV)
* Bottom balance (let's not go there)
* Continuous balance
For years I'd been using my PowerLab8 charger (designed for radio-control battery charging) to charge my 2P8S pack on my scooter and my two larger 4P8S Headway (LiFEPO4) packs for my electric outboard and standby power system. The PowerLab8 uses a continuous balancing technique with a wonderful graphic display showing the voltage level of each paralleled cell group, how much current is being bypassed for each cell group, and how it changes over time as the pack is charged. Great multi-colored cellvoltage vs. time graph display on the PC showing how the diverged pack voltages gradually converge during the charging cycle, and this now-single graph continuing to rise to the programmed voltage level (fully selectable) and decaying current over time.
There are some massive threads discussing this topic on the Tesla Motors Club forum, with the leading expert (who disassembled the Tesla pack and performed a whole bunch of measurements) stating that a brick doesn't start balancing until it reaches 93%. I buy that. If anyone is interested in what the Tesla pack looks like, here's the link:https://teslamotorsclub.com/tmc/threads/pics-info-inside-the-battery-pack.34934/
On the other hand, when charging at the various Tesla Service Centers around the country, I've been asking this same question and have been repeatedly told (if the person I was talking to understood the question) by the service people that the Tesla continuously balances the pack, with no need to fully charge it to obtain that benefit.
Like I said, lots of discussion on the TMC forum, with very little brick voltage drift being noted.
For myself, just before my next Tesla trip I do indeed intend to perform a carefully-timed very long slow (using 120vac) charge to 100%, thus ensuring a balanced pack no matter what. First, I'd like to obtain the hardware and software (like CaniOn and LeafSpy) which shows individual brick voltages so I can see what's going on inside.
In the meantime, the Tesla is back in the garage under its cover sitting unplugged at 40%SoC with a float charger hooked onto its 12v battery, while I enjoy driving my i-MiEV around town. Like I said before, best of both worlds!