I know a little bit about batteries. At the risk of being smug I'll ask if you charged it first. If it was fully charged and it didn't last as long as it was supposed to you should ask for a refund. Quality control on cheap Chinese lithium batteries is spotty and it isn't unusual for the batteries to underperform. Temperature will also affect battery life, so if it's cold you should expect shorter operating life.

I only use rear lights on blink and just bought a second one for backup in case I forget to charge my main light.

edit: just saw your post. I only use my lights when it's dark and I think they're more effective blinking. 2 hours would work for my daily commute if I wanted to leave it on steadily. That's not much different than my front light which I usually charge every day and it has a large (4.6 Ah) battery.