Is he lying

my husband went to the shops to get something for tea. i thought he was gone awhile considering he only had to get a few things. he came back and i said he had been gone for a while and he said he hadnt. i joked that he must of been emailing his fancy woman not knowing that he had took his works phone with him. then he said he got a works email so he was doing that as it was for an order. i always say he as another woman but he denies he as ever cheated and only wants me. the next day he said he was charging up his phone to not use the electricity in the house as there wasnt much left on it. i thought it seemed strange him saying that because there is still enough electric on the metre and it wouldnt use much to charge up a phone. i dont know what to believe.