I thought there was a recent post looking for battery cover and slip case for a Voyager, stating that they were no longer available through the HP website - I can't find the post now, but I went to HP Parts Direct to see what I could find. The 12C no longer shows up in the "Partsurfer" which is used to find part numbers for a particular model. The 48G does show up. Then I went through a stack of postit notes on my table because I remembered looking up some HP parts in the past, and if I knew the P/N I could skip the Partsurfer. Well, it turned out the P/N I had was for the Pioneer slipcase. Just for fun, I tried putting my 12C in a Pioneer slipcase and it fits great! The slipcase is just about 10mm too long and the notches that let you grip a Pioneer to pull it out allow the opening to flare out a little to let you grip the Voyager. Maybe HP had this in mind?
So I entered the P/N 82243-60001 into the parts order system:
https://parts.direct.hp.com/ShopForParts.asp
and it shows out of stock but lets me order it. Best of all, the price is $3.40 - it had been $6.00. However, when I placed the order, there was a shipping charge of $12.67! It used to be that all prices included shipping. So - no order. (Maybe I told the story of my $0.11 FedEx shipment too many times!)
But, if anybody has part numbers for the Voyager battery cover and slipcase, we could try them at the website above to see if they are still available.