I have a large 20s 10p battery that takes ages to charge with my 84v 5a charger. I've seen people build fast adjustable 20a chargers with a 1800W DC DC Boost Converter Step Up, a power supply and some fans for under well under 100$. chargers like these are usally insanely expensive, except for this one:
www.aliexpress.com/item/1005002433424642.html?spm=a2g0o.productlist.0.0.3b 6e4405kUpwiH&algo_pvid=bead39dc-2ee0-413a-97c8-007d963f2cb8&algo_exp_id=bead39dc-2ee0-413a-97c8-007d963f2cb8-2&pdp_ext_f=%7B"sku_id"%3A"12000020638422207"%7D

Is it worth building your own when this cheap charger is available and does anyone have any experience with cheap fast chargers from China and have wise advice on which charger I should get / build?