Here is the page that talks about it from the R1 manual;
You need to open up the controller to change the battery, so yes, you may lose your RAM backed data, but if your program is stored in flash (which it should be), then you won’t lose that.
(Hint, use PAC Terminal to inspect the controller and see where the strategy is stored).
Please take a look at the date code on each of your controllers… As you can see mentioned, if its manufactured before July 1st 2007 the battery is not a rechargeable type which just means you need to be mindful of what type of battery you replace it with.
From chapter three of the same doc we get the replacement part number (for the rechargeable type).