Response security alarm?

I have the code, but the previous owner did mention it didn't work,so over the weekend I decided to see if I could get it working again for my own use.I plugged the transformer in and immediately went off.The code given did silence it but it showed low battery.I left it overnight thinking the batteries needed time to charge but the alarm went off in the early hours.Again the code silenced it,so yesterday I replaced the 6v battery for the control panel the two batteries in siren on the wall outside the 9v batteries in all three pires and the two 3v batteries in the magnetic door contacts.The problem is it still shows low battery,there's nothing else that needs batteries?,is there a set procedure for battery replacement or can anyone help please.