Upgrading lead acid battery

[Travis2691]

I’ve brought a 1000w 48v 20ahp quad bike but the run time is only 45 mins can anyone advise what battery , charger etc to use to upgrade to get longer running time.

 

[E-HP]

In general, you’d want a bigger battery for longer running time, but only you know what you mean by longer.
What’s your budget?

 

[Chalo]

Here's one that needs BMS and a charger that tops out between 52.0 and 54.6V, but it will more than double your existing range. It also weighs less than half compared to what you have.

48v Audi Q5 PHEV modules, Zero Miles Samsung Cells | JAG35.com Jehu Garcia DIY Powerwalls Lithium Ion Batteries EV eBike eScooter Emergency Solar Off-grid

PLEASE READ THE DESCRIPTION CAREFULLY. Shipping to Lower 48 USA states only via Ground Shipping. No shipping to PO Boxes. No international shipping including Hawaii, Guam, Puerto Rico. Non-USA customers click here. EV modules with high quality Samsung cells! These 48v 37Ah 1.78kWh li-ion modules...

jag35.com

37Ah is not quite double the nominally 20Ah of your existing pack, but I can assure you you're not getting anywhere near 20Ah now. A lithium ion automotive module like the one in the link suffers much less Peukert effect, and tolerates deeper discharge without as much loss of capacity.