Hi PJ, You need to open the cover on the top side of the pack using 2 phillips screws and pull the plastic tab underneath down to release the cover, you will then see the 2 batteries, these should slide out after removing the support bracket, otherwise the pack will need to be run off, if you need any further assistance with your Minivatior, please contact me at, onestepengineering(at)hotmail.com, service/spares/repairs available, hope this helps, Many thanks
One Step Engineering, October 2012