Tektronix Applications Expert

The THS720P will work find plugged in with out a battery. +12 DC, 1A,; 2.1 ID, 5.5 OD.
More information in the manuals.

A web search for the battery could show a few places with replacements but I can't recommend any or know anything about them.
Battery was BATTERY PACK; 4.8V, 2.8AH;NICAD, 4 C CELLS IN SERIES, 1.05 X 7.78,

The best replacement for the current capability is the Model 6430 source meter.
It can source current from 0.1A to 1e-17A.

Link below to the data sheet:

https://www.tek.com/en/products/keithley/low-level-sensitive-and-specialty-instruments/electrometers

TPP0101 as compatible probe for the 2235. See more info here:

https://www.tek.com/en/datasheet/passive-10x-voltage-probe-0

If you are interested in placing order or pricing, contact sales at 1.800.833.9200 or email the request to buy@tektronix.com.

Please contact Tektronix service team directly. Below you can find the contact Ask about insurance against accidents as well if you want to protect your instruments.
Tektronix/Keithley Repair/Calibration:
Web: https://www.tek.com/en/service-quote
Email: rmarequest@tektronix.com
Calibration services for all other products:
Web: https://www.tek.com/fastquote
Email: mvs@tektronix.com

Please contact Tektronix service team directly. Below you can find the contact Ask about insurance against accidents as well if you want to protect your instruments.
Tektronix/Keithley Repair/Calibration:
Web: https://www.tek.com/en/service-quote
Email: rmarequest@tektronix.com
Calibration services for all other products:
Web: https://www.tek.com/fastquote
Email: mvs@tektronix.com

Please contact Tektronix service team directly. Below you can find the contact Ask about insurance against accidents as well if you want to protect your instruments.
Tektronix/Keithley Repair/Calibration:
Web: https://www.tek.com/en/service-quote
Email: rmarequest@tektronix.com
Calibration services for all other products:
Web: https://www.tek.com/fastquote
Email: mvs@tektronix.com

Please contact Tektronix service team directly. Below you can find the contact information for our Service Department and someone will be happy to help. Ask about insurance against accidents as well if you want to protect your instruments.
Tektronix/Keithley Repair/Calibration:
Web: https://www.tek.com/en/service-quote
Email: rmarequest@tektronix.com
Calibration services for all other products:
Web: https://www.tek.com/fastquote
Email: mvs@tektronix.com

Please contact Tektronix service team directly. Below you can find the contact information for our Service Department and someone will be happy to help:
Tektronix/Keithley Repair/Calibration:
Web: https://www.tek.com/en/service-quote
Email: rmarequest@tektronix.com
Calibration services for all other products:
Web: https://www.tek.com/fastquote
Email: mvs@tektronix.com

Please contact Tektronix service team directly. Below you can find the contact information for our Service Department and someone will be happy to help:
Tektronix/Keithley Repair/Calibration:
Web: https://www.tek.com/en/service-quote
Email: rmarequest@tektronix.com
Calibration services for all other products:
Web: https://www.tek.com/fastquote
Email: mvs@tektronix.com

Please contact Tektronix service team directly. Below you can find the contact information for our Service Department and someone will be happy to help:
Tektronix/Keithley Repair/Calibration:
Web: https://www.tek.com/en/service-quote
Email: rmarequest@tektronix.com
Calibration services for all other products:
Web: https://www.tek.com/fastquote
Email: mvs@tektronix.com