To prevent the lowering of the life performance of a negative electrode plate under a high temperature by adding bisphenols and sulfite or amino acid formaldehyde condensate to an active material.

The polymer average molecular weight of bisphenols and sulfite or amino acid formaldehyde condensate added to an active material is preferably 0.3-3.0×104. This condensate is preferably added along with a derivative of naphthalene sulfonic acid formaldehyde condensate. The condensate is preferably added along with lignin or its derivative. More practically, this condensate is a condensate of bisphenol A, sodium sulfite and formaldehyde. This constitution improves the life performance especially under a high temperature so that it can be applied to various kinds of lead-acid batteries and used for various kinds of utilizations.