Measure the total voltage of the batteries during float charge (or trickle charge). If the charging equipment provides an incorrect reading, be sure to investigate the reason behind any deviation from the specified voltage range.
Check the batteries for any sign of irregularities in appearance or damage such as a crack or deformation, or if electrolyte leak is found on the case cover etc. The batteries must be replaced with a new one. Also, clean the batteries if these are found to be dirty due to dirt and dust.