Siemans wireless heating controller battery usage?

Hi, We have a Siemans RDJ10 wireless remote to control our central heating. It was fitted June 14 since then we have had to replace the batteries every 6 to 8 weeks. Have even bought Duracell rechargeable batteries as it was costing so much in battery replacements. These are now only lasting a couple of days. Thought this was just the price you have to pay for this type of device but a recent heating engineer said the batteries should be lasting much longer. Has anyone else experienced this problem? Is this device faulty?

Karen
September 2015