Actually, if you think about the voltage, then yes, discharging
more than a few percent is bad.
A 2.7 volt cell should not be discharged below 2.5 volts,
thats about 8%.
You can still discharge lower than that, but it shortens the
battery life.
I once set my SLA charger up on a timer to charge every 15mins and off every 15 mins for 8 hours. Four hours on and four at rest in total. When I woke up the next morning, All my batteries were fully charged, in balance and discharged in balance too.
I have some theory in the works.
I will post it when I can understand how to explain best, that the more voltage drop over each cell equates to less resistance due to charge storage/
With resistance, more resistance usually equals more voltage drop.
Inside the cell this is opposite. Like a mirror. Voltage drop from one cell to the other indicates charge state not internal resistances. This may allow me to understand why higher voltages to the pack don't charge batteries faster than current, yet I have observed that using a higher voltage seems to make cell voltages vary wider. This sounds like a bad thing, may be not. As we observe that the smaller V drop on any cell indicates the lower charge state so to the wider voltage differences between cells may indicate better charging of the lower charged cells. The actual charging voltage into the cell is higher the more variance you can achieve between cells with the nominal pack.
What I mean is that, if you put a 56v charger on a 48v pack it will charge fine if balanced, but if it isnt balanced, try putting 72v @ 1 amp on the pack and you will see larger voltage variances between low cells and high cells. This can let the
BMS work better as it can sense the larger voltage differences between a low charged cell and a full charged cell.
It must be rated under 80 watts so this allows time for the energy and
BMS to work its job.. The pack must be cut at HVC at the rated pack voltage regardless of the 72v input voltages so no damage is done to any cell and one must watch the cell voltages like a hawk.
Other wise try the timer at bulk mode voltages as you will notice at the beginning of the charge the same anomalies I described above larger variances of cells voltages every time the timer charge kicks in. The full cells will be higher and the low cells will be lower.
I am scared to tell people to put 80v on there packs as you know what could happen if it left on too long. And just as scared suggesting the timer method I have used with my SLA's.
I just tell people to leave it on for days and hope the trickle will balance things out.
Edit:
Surface charge can have no time to be absorbed when the variances are so little and trip the charger off earlier. Where as at higher voltages one will observe strange balance behavior not yet described or defined by anyone I have seen yet.
On the 48v SLA's I balanced with a zener shunt looked scary with a 72v input. The fuller capacity would rise sharp and then emptier battery responded by picking up the charge potential. As the lowest charged battery was the highest resistance it had more voltage potential over the terminals.
After not too long the voltages would rise up like a Mexican wave along the batteries finding any missing capacity in the lower cells.
