Alpena Jeff said:Please explain this statement.
Simply put, the main issues arise from cable,connection and internal impedance, if we eliminate cabling and terminal contact
variances ( very difficult for DIY as you don't have the equipment, but achievable ) we are left with internal impedance ( apparent resistance of the battery ). this is quite variable, certainly more so with AGM
Now, a battery with a higher impedance will, over time, result in less charge current to that battery, thus resulting in a lower average
SOC ( state of charge ), this has the effect of aging the battery and increasing its internal impedance. over many cycles the effect becomes more pronounced. when the battery pack is idle ( minimal load ) other batteries in the string of higher SOC will discharge into the lower SOC battery and self equalize the voltages, but, this effectively makes the whole set equal to the worst battery in the pack.
this just gets worse as we add more batteries to the string, the net result is shorter lifespan and capacity due to all the unequal current flows.
with FLA these effects can be mitigated somewhat by periodically charging with an equalizing charge for an extended period, but as we know, equalizing causes more plate corrosion and reduces life.. !! we only equalize to reduce sulphation and electrolyte stratification. with agm, you can't equalize, so you have to hold at float for at least 24 hours to get the SOC to balance somewhat.
other issues with parallel FLA include cell shorts, imagine what happens when one cell shorts in a parallel bank.. the other batteries discharge into the failed battery and that's going to give you a very bad hair day with fire, smoke and hot acid !!!
now, with eight agm's having lower and more variable internal resistance, the owner has no way in hell of ever balancing the charge currents, I know this from experience actually measuring charge and discharge currents on parallel strings, it just ain't gonna happen..
so again, the net effect is much shorter life and reduced capacity. all at a 200% premium over FLA.