The stock battery in a DRZ400 is the Yuasa YTZ7S which can be replaced with a NOCO NLP5. You will need to ensure that you have a battery tender that can put out 14.6 Volts and respect the max charging current for your new battery!
In my case I have a much bigger battery because I removed the decompression system from my camshafts. The biggest battery you can put in is a YTZ10S and it will take a bigger max charge rate than the NLP5. This bike has a Sisneros battery bracket but I'm sure you could make something on your own.

DRZ400 DRZ400S DRZ400SM HOW TO DIY

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NOCO Batteries
-NLP5, max charge is 6 amps, https://amzn.to/3un6z3J
-Noco 5 Amp Charger: Genius5, https://amzn.to/2VOzr42
-NLP14, max charge is 12 amps, https://amzn.to/353H27j
-Noco 10 Amp Charger: Genius10, https://amzn.to/3mWMA74

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Battery Charger Video:
   • NOCO NLP Lithium Batteries Require 14...