What about lifepo4? Less fire risk than Li-on. Pings packs are pretty reasonable.
24V is the lowest standard pack but he builds custom packs too. Well regarded in the e-bike community, he stands behind his work and builds solid and reliable packs.
Leadtime: 7 days
It will take about 7 days for us to build and test this new battery pack for you.
Suitable Wattage of Motor: up to 800W rated motor, 600 Watt suggested
Applications: E-Bike, Electric Bike, E-Scooter, Electric Scooter
Voltage: 24 Volts
Capacity: 30 Amp Hours
Dimension: 300x105x150 mm / 11.9x4.1x5.9 inches
Weight: 7.50 kg / 16.5 lbs
Charging Voltage: 30 Volts
Charging Current: <10 Amps
Rated Discharging Amperage: 30 Amps
Max Continuous Discharging Amperage: 60 Amps
Maximum Discharging Current: 100 Amps
Discharging Cut-off Protection: 75 Amps
Lifecycle of the whole pack: >85% capacity after 1000 cycles. Lifecycle of single cell: >85% capacity after 1500 cycles, >70% capacity after 3000 cycles. (<1C discharge rate and <1C charge rate)
Or alternatively, Golden Motors (goldenmotors.ca) makes some good large batteries, they use large flat cells IIRC. They are typically 48V, but can also build custom packs as well.
Both in the standard car battery format(to fit exisiting systems) and in stainless rectangular columns(wires at top)
48V20AH and 30AH respectively
Pricey but if you are short on space, or you need something that AGM can't do they might be a good option.