[MrFixr55]

Hi Matt,

"Radio C Batteries" (Not to be confused with "Size C" 1.5V Batteries) were used with early battery sets from the early to mid 1930s, especially with ones using the 2V tubes like yours, and are definitely not available in working condition.  This was a package of several batteries in series with connections for the desired voltages that were, in fact, "taps" on these batteries. Since minute amounts of current were drawn from these batteries, they often lasted the life of the radio.  Here is a picture of the battery that may have been used for this radio.  It was used in my 1936 RCA 6BT and 1937 RCA 5BT:
   

To replace these batteries is relatively simple.  Your radio needs 2 "C-" voltages; -3V and -7.5V. This is done by having five 1.5V AA Cells in series with a tap on this "battery" for -3V.  I have done exactly the same thing on 2 RCA Farm sets; a 5BT and a 6BT.  This is done by doing the following:

• Obtain a battery holder for 2 AA batteries and a holder for 3 AA batteries from eBay, Amazon, local suppliers, etc.
  
• Connect the positive (red) lead of the 2 battery holder (3V) to the A-B-C+ connection (likely chassis ground).
  
• Connect the negative (black) lead of the 2 battery holder AND the positive (red) lead of the 3 battery holder to the -3V "C" lead on the radio.
  
• Connect the negative (black) lead of the 3 battery holder to the -7.5V "C" lead on the radio.
  

There is practically no current flowing through these batteries when the radio is powered down, therefore, there is no need to have a switch between the batteries and the radio.  These batteries should last to their expiration date.

Hope this helps.