The lower voltage battery with the same amp-hour rating will have less capacity. This not only means less range, but more frequent recharging. Since batteries are only rated for so many charge cycles this also means you will be replacing it sooner.

The earlier post about those voltages becoming obsolete will matter when it comes time to replace the battery, Choices might be limited.

By the way IMO the best way to prevent battery theft is to take it with you. Mine mounts with magnets and comes into the store with me. I've read articles saying key locks are easy to smash. The thief then buys a replacement shell for cheap.