I run a 1986 QT10 with a T1. I have changed the batteries out several times in the past. All I do is turn the machine on and then replace the batteries and then leave the machine on for 24 hours after that so the new batteries can charge up. I also have a copy of the paramaters on paper just in case. I have never lost any parameters doing this type of batterie swap.
most controls will allow you to pull mem board to remove any hardware holding batts BUT DONOT disconect battery until you plug board back in and turn on machine. again be sure to back up parameters,macros programs offsets ect. saves a lot of heartache. This info only works if your battery has enough juice to keep mem with board out