I have a large array of solar panels, which are 12v panels. I have wired them two each in series to produce 24v at the array and carry that to a 24v charge controller which then connects to two 12v batteries wired in series for 24v, to power a 24 volt inverter. But I have observed a problem with this configuration. The problem is that while the system is still charging up the battery bank, if I separate two batteries and measure the voltage on them, the first in series (from the + connection end) will be fully charged at 12.6v and the second will be less. For example, when my voltage on the array shows 28v during charge, two batteries separated and tested for voltage may show one to be 12.6v and the second one at 10.8v. This means to me that one of the batteries is being overcharged while the other battery is not yet charged. It usually results in the first battery of the pair failing. Never the 2nd one. I am not certain but I get the feeling that the cause of this is that the power coming in to charge the batteries must pass through each cell to get to the next? Whatever the cause of this is, it causes battery failure as the first battery in line in the series configuration gets overcharged while the 2nd battery is still charging to get up to full potential. After consideration of this problem recently, I wondered if it might not be better to carry the common between two solar panels on the roof and tie it to the common (+/-) post that tie the two batteries together. In this way both batteries would see 12v from the array and charge simultaneously, rather in a cascade fashion. The solar controller would still control the charging of the array as both the + and - of the array go through it, so when it turns off, there would only be the common leg connected directly to the solar array, hence no path for power to bypass the charge controller. Likewise the inverter would not change it's connection and would still see 24 volts. I would like to understand the cause of the difference in voltage (is it really due to charging in a cascade fashion?) I know that it is not a bad battery issue, as I have twenty 265Ah batteries in the bank (10 banks of two batteries each) and all batteries show the same voltage when tested. So it's not just a battery going bad.