Im' not sure if this is what you are already doing but I will suggest it to make sure.
Make or buy your batteries in a flat side by side configuration and it will be easier to make chages in the future. To add batteries just solder them on. and visa versa. I really don't like stick packs my self. I wish they didn't put the "battery holder" in the SV in the first place. My flat packs don't fit that well in the SV battery holders. I found that in my Aquajet Exteme from offshore, the hook and loop system worked just fine.