pretty sure three 12v 100ah battery doesnt give you 36v 300ah
its still 36v 100ah or 12v 300ah, depending how you wire it i guess
edit*
https://www.se.com/pt/en/faqs/FA229757/
Battery bank assembly; amp hour calculation
Published date: 15 April 2020
Issue:
This article is designed to give basic information on how to connect batteries together in a bank and then to calculate the amp hour capacity of the bank.
Product Line:
All devices requiring battery banks
Environment:
All units with external battery banks
Resolution:
1. two batteries can be connected in either "series" or in "parallel".
1a. "series" is when we connect the battery poles in a positive to negative orientation.
1a. when in series we add the voltage and average the amps
1b. "parallel" is when we connect the battery poles in a positive to positive and negative to negative orientation.
1b. when in parallel we add the amperage and average the volts
eg. when taking two 6 volt, 100 amp hour batteries in series, it becomes 100 amps at 12 volts. When in parallel, it becomes 200 amps at 6 volts.