These are no longer available. KEEP your old one and remove the connector and wire so you can make your own replacement battery pack. AA nicad batteries with solder tabs are available by searching the internet.
Fits the ELENCO F2800, F2850, F2700 and F2900 and the B&K 103, 104, & 106 Frequency Counters
600mAH NiCd Battery Pack 4xAA