The 52-year-old had held the role at the water and energy group for six years but was not offered the top job when it became available.
United declined to say whether Mr Batey applied to be chief executive, but insisted his departure was "very amicable". He will stay for the next six months before leaving after the annual shareholder meeting on 31 July.
Mr Batey was paid a salary of £340,000 last year plus a bonus of £193,000. He will get a further six months' salary when he leaves, United said. Other payments will depend on the performance of the shares.
There was slight unease in the City at the prospect of the company lacking a finance chief. Sir Richard Evans, the chairman, praised Mr Batey as "the architect of the innovative two-stage rights issues which raised £1bn for investment in the business".
Philip Green, formerly of P&O Nedlloyd, arrives as chief executive designate in two weeks. He formally takes over at the end of next month. United shares rose 19.5p to 700p, leaving the company valued at about £5.9bn.Reuse content