Siemens C61

I have the CT56 right now and looking to upgrade to either this phone (C61) or a Motorola V551. Gotta have a speaker. I have been pleased with my CT56 and was wondering if anybody knew if the batteries and charger were interchangeable between the ct56 and the c61? it was written that the speaker is BETTER (louder?) than the ct56? Is this true? any help appreciated!