Ok - the results are mixed after the overnight discharge.
The Good News:
When I went to bed all the packs had already balanced to 4.1V
So that is good....
The Bad News:
Letting them sit overnight actually *imbalances* the packs due to the quiescent current draw of the units. First they balance perfectly... then the draw to keep the LCD screen etc running runs things out.
Now to put it in perspective - that is not that bad of an imbalance. 4.101V - 4.083V = 18mV
That is nothing to be pleased with - but it is certainly a reasonable number. Those of us who have been running lipo for a few years (and abusing lipo...) know that it is pretty common to have a bank of cells out by 100mV or worse - especially after a few deep discharge cycles. If you told me my pack would never be outside of 20mV per bank - I would be totally satisfied with that.
Truth is - most guys don't even have equipment accurate enough to measure that type of difference with any sort of accuracy
Many may think they do, but that is just because they have not actually calibrated their equipment against something that is truly accurate to 1mV or less.
The News to make you feel a little better:
To be fair, these were little 4S 5Ah packs. In reality you would be balancing a 10Ah or 15Ah pack so the "imbalance" would be a lot less... most likely in the 10mV range
A great option here would be to have a trickle supply set to 4.1V/cell.
For instance - with an 18S pack you might have a 73.8V 200mA supply.
This would keep the packs up.
This type of supply is actually quite easy to make and often looked over. Most people would never consider a bulk charger that works at only 100mA or 200ma.... but actually it makes a ton of sense for an application like this. There are many junk supplies out there that can put out 0V to 100V at low current.
At this point my plan is to just hook them up when I get off work and unhook them when I go to bed. That is a solid 5 hours - and if you do this for 2 or 3 days your pack will absolutely come into reasonable balance.Now....
Lets talk about getting a little more performance out of these....
P.S. None of my plastic was even close to being melted - though these were 4S packs to be fair. Those with melted plastic - try to measure the shunt power if you can.