LONDON (AP) _ Hanson PLC, the huge British industrial conlgomerate, said Monday it has agreed to sell its British battery company, Ever Ready Ltd., to Ralston Purina Co. for $228 million in cash.

St. Louis-based Ralston Purina already owns Eveready Battery Co. in the United States.

The purchase will reunite the two companies after 78 years. In 1914, Eveready Battery Co. was sold to Union Carbide Corp. and Ever Ready Ltd. was sold on the British stock market, Hanson said in a news release.

Hanson said the sale was subject to regulatory approval and didn't include Ever Ready Ltd.'s operations in South Africa.

Ralston Purina Corporate Vice President J. Patrick Mulcahy said in the news release that the purchase ''fills a major geographical gap in our markets.''

The U.S. Eveready arm expects to use its technological expertise to help the British company broaden its product range, Mulcahy said.

Hanson said that Ever Ready Ltd. had pretax operating profit of 18.5 million pounds, or $33 million, on sales of 87.1 million pounds, or $153 million, in the year ended Sept. 28, 1991.