Laptop wont boot with battery in

Hi Guys and Gals,

Starnge issue this, i have discovered my laptop wont boot with the battery in. It has only started in the last couple of days. The battery that was in has been showing that it was coming to the end of its life for a while now but i have just left it ru nning on mains. I bought a new one ( OEM ) some time ago to replace it but havent used it. But even when i put the new onre in  i have the same prob. Laptop switches on, but just black screen with the whirring noise in background. If i boot without battery there is no prob but as soon as install batt, laptop crashes. Any ideas? Im not fussed if cant be resolved as i will use on mains, just a bit frustrating.