How difficult would it be to replace the battery compartment on a set of PVS14?  Who has the two battery boxes?  All I've seen are the single battery upgrades.  

Thanks!

The dual battery 14 housing was discontinued in favor of the single battery housing which is much better IMHO. Some dealers may still have the dual battery lower housing in stock but I don't know why you would want it. The single battery will work just fine with the older style and has a few improvements. TNVC sells them. Just look under night vision parts. Around 3 bones for the lower single battery housing.

Pretty easy upgrade to do yourself but you will lose your nitrogen and if you live in a very humid climate it should be nitrogen purged. I assemble my scopes on very low humidity days and never have any issue.