What configuration of batteries are you using, as in 12 X 2V, 2 X 12V or something else?
If your regulator has a meter to tell you voltage at any given instant you might notice during charging [with a constant level of sunlight and no clouds], some small fluctuations up and down. This is a fair indicator that one cell is having some internal problems, while the regulator will do it's best to keep the total voltage where it wants it. If you've got a meter you might be able to pick a failed cell even with the whole set connected. It can be at a lower voltage than the rest [in which case the regulator will ask the rest of the set to achieve a higher total individually and combined] or again, it could fluctuate. If it does, the fluctuations can be quite significant. I had a failed cell in my set that ranged from close to 0 volts to nearly 5 volts.
Last edited by jules
on Fri Feb 10, 2017 11:06 am, edited 2 times in total.
Primary system: .8KW Trina panels; Plasmatronics PL40; 1,000Ah VRLA 12X2V battery bank; 1.7KW Selectronic inverter
Veteran system, semi retired: 6 X 55W Solarex 12V panels; Fangpusun CC; 6 X 2V, 35 year old 550Ah lead acid flooded cell batteries.