WHAT? you have lead acid batteries( hydrometer ) and you have not checked them in 2 years?
That is a good way to kill Pba batteries quickly. It is SUPER important that the liquid acid level never go below the tops of the lead plates. You really should check the fluid levels before the next charge, if low bring it up half way between the plates and the full mark, then fully charge and then top off the acid level to the full mark. And only use distilled water.