Are you asking if higher capacity 10440s exist? I have some that are 500mAh I believe.... I can't find them right now, but pretty sure they're 500mAh.
Not really sure what your trying to find out. Are you worried higher capacity
batteries won't work or something? Any 10440 will work in your eCab. They are all the same voltage, so you won't gain any power by switching to a higher mAh battery.
The mAh rating is just the capacity, or how long the battery will last between charging.
Hopefully this got somewhat close to answering your question, if you need to know anything else feel free to ask!