For batteries I've really good luck with this brand on Amazon:

https://www.amazon.com/gp/product/B07SYNLFB5?pf_rd_r=CCPF6536JHPJ8MDNB5GB&pf_rd_p=8fe9b1d0-f378-4356-8bb8-cada7525eadd&pd_rd_r=a6bb944a-9a26-4eec-86c7-a472214ae082&pd_rd_w=LomEr&pd_rd_wg=An82u&ref_=pd_gw_unk

I don't run this exact pack but I run the 4s 6500 version in my XMAXX and they are great for the price. Highly recommend changing all your Traxxas connectors to XT90 down the road too.

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Battery charger I am running this:

https://www.amazon.com/Venom-Battery-Balance-Charger-%E4%B8%A6%E8%A1%8C%E8%BC%B8%E5%85%A5%E5%93%81/dp/B01IDNJ5PG/ref=sr_1_3?dchild=1&keywords=venom+dual&qid=1632270185&sr=8-3

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Battery disharger I am running this:

https://www.amazon.com/SKYRC-BD250-Battery-Discharger-Analyzer/dp/B087NFJN67/ref=sr_1_9?dchild=1&keywords=lipo+discharger&qid=1632269928&sr=8-9

I consider this optional honestly. You can just run the car and discharge the batteries too. A discharger on the above charger also works but takes a painfully long time. I have a lot of batteries and multiple cars. I'll take a few cars out with fully charged batteries with friends and sometimes we wont go through all the packs so the discharger is nice to have and discharges the battery a lot faster.

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Hope this helps!