Yes the "maintenence free" Antique Auto batteries are the sealed small battery inside the casing of your choice...Antique's battery caps can be spun off and that sealed battery can easily be seen inside the casing...

Next step would be to find a cost effective battery to use in the casing...Not long ago a suitable battery might cost more than the complete unit you're trying to replace.

Now, with the battery prices going up without any competition in place it might be worth the effort..