Suddenly our agm batteries (2 rows of 4, set up as a 48volt system, each batt.135ah) are making the dreaded bubbling noise while absorption charging. They are only a couple of weeks old, and barely used. They replaced similar batteries, but these ones are dual purpose, i.e. could be used for starting a vehicle ase well as for deep cycle purposes. We hadn't changed any settings on the 150/60 Blue Solar mppt, but it was the first time I ever heard the bubbling. We reduced absorption voltage to 56v, and float to 54v during the bubbling, and it stopped, but then we used a hot plate, and charging changed to bulk, and when it went back to absorption the same bubbling noises started, so I further reduced the voltages, with float now at 53v and absorption at 54.5v. Once again, the bubbling stopped, but who knows what will happen next time a load is applied and it goes to bulk, then absorption, and possibly triggers the bubbling before float kicks in. The highest current we observed during all this was 8 amps, and towards the end, before I intervened with voltage reductions, 3 amps. I thought bubbling would only occur at high charge voltage/amperage. I also read somewhere that something called sulfation can occur if charge voltage is not high enough. What could go wrong with the lower voltages I've now set? It's like choosing how to die: lose the batteries through cooking away the electrolyte, or lose them through sulfation. Documentation the manufacturer provided indicates that the original higher values the mppt was using would be fine, so I don't understand why this problem has suddenly arisen. Can anyone help, please?
