In many ways the battery holder is easier. You get them from an electronics (or decent computer) store (we have Jaycar here) and you need one that mounts flat (parallel to the PCB), or as I said just buy it from MJMP. Regardless the old battery has to be de-soldered and removed. You can get batteries (3v lithium) with the lugs in the right place (all the ones I've seen here in stores are in the WRONG place). It is possible to solder wires onto a battery and do it that way but NOT recommended. MikeB did this and it wasn't easy (he said) not to mention heating the battery up with a soldering iron to make the solder flow isn't a good idea, lithium batteries don't like to get hot LoL. You can also get a battery with lugs attached and solder wires to the lugs and then to the PCB, it will work but isn't very tidy/elegant.