As noted here, it seems much better to get a CharlieCard rather than a CharlieTicket. Unfortunately, I didn't know this and bought a stored value CharlieTicket. Is there any way I can transfer the amount in my CharlieTicket into a CharlieCard instead, so I don't pay the higher ticket prices? Will the fare machines let me do this?
As usually, the MBTA is quite obtuse about this. Apparently this did work at some time (http://charlieonthembta.blogspot.com/2006/12/now-can-you-transfer-funds-from.html) but there is no current information whether this is still the case or not.
They are pretty clear that you can't redeem the remaining value of a Charlie Card for cash. It's a pretty devious system actually: the Charlie Ticket subway fare is $2.65 and the smallest default value at the vending machine is $5.00 (although you can select "other amount"). There are probably quite a few Charlie Tickets $2.35 remaining value been thrown away.
Your best shot is to go to the Charlie Card store in Downtown Crossing and ask.
At least as of 2022, you can do this via mail using the "Consolidate cards or tickets" process listed at https://www.mbta.com/fares/charliecard