If you're going lithium, this is the best deal I've found. With Cam and BBK usually the extra power is handy to have.
Amazon.com: Tusk Lithium Pro Battery TLFP-7L For HONDA Monkey 125 2019-2020
Buy Protek YTZ5S YTX4L-BS YT4L-BS YB4L-A YB4L-B 12V 4Ah Sealed AGM Gel Type Battery MF Factory Activated For 2014-2017 Honda Grom 125 MSX125, 2003-2005 KTM EXC Racing 525 520 450 400 250 at Amazon. Customer reviews and photos may be available to help you make the right purchase decision!
and something cheaper
Buy YTX4L-BS - 12 Volt 3 AH, 50 CCA, Rechargeable Maintenance Free SLA AGM Motorcycle Battery: Batteries - Amazon.com ✓ FREE DELIVERY possible on eligible purchases
I would measure stock battery compared to these and verify Pos post are on the correct size.
I've purchased many batteries through Amazon and you can take your core to an auto parts store and receive a $10.00 store credit in most cases.