Have batteries gotten to the point where they will hold at least 2500 watts yet? Cost? Weight?
Most ebike battery packs do not get too far over a kilowatt because the pack alone is going to weigh in at over 9kg (20 pounds). Once you get to 1000 watt hours, its called a one-kilowatt battery pack, and that’s how electric car packs are measured. 2500 watt hours for an ebike battery is going to weigh in at over 22.5kg (50 pounds) and you're completely leaving ebike territory and moving into electric car territory.
One of the things to look out for is that ebike sellers can sell you on a
high Amp-hour pack, but miss the fact that it's actually
low voltage. For example a 36 volt 10-Ah pack does not have near the range of a 52V / 10-Ah pack. To do a comparison on ranges of two different battery packs, they must be the same voltage, in which case all you would need is the Amp-hour rating to compare the difference. But…if the two packs are two different voltages then you must calculate
Watt-hours. Watt hours are calculated by multiplying the batteries volts by the batteries Amp-hours. A 36 volt 10-Ah pack has 360 watt hours and a 52V 10-Ah pack has 520 watt hours.
Once you know how to calculate watt hours you can fairly well know what you are paying for in an ebike battery pack!