Any budget portable headphone amps which can double up as a power bank for your DAP?

[PCA]

While going through the marketing material for Topping NX1S headphone amp, I read that the battery gives 40 hours of playtime. That is significantly more than the claimed playtime of most DAPs. That made me wonder whether there are any portable headphone amps out there that could double up as a power bank for your DAP.

Anyone aware of any? Especially in the budget price range of < Rs. 5000?