Securing batteries in forward compartment (Security)

A heftier lock will not be a deterrent, they'll just pop the baggage door open with a medium sized screwdriver. You'd have to make sure the new lock looked the same as the old lock, or that calls immediate attention to the fact there's something worth protecting in there.

Perhaps an intrusion alarm that will call your cell phone would be an option. They aren't horribly expensive, and could give you a chance to call someone to check things out.