Battery pack as PS?

I tried searching but couldn't find any information about using batteries to power a dac and headphone amp.
I'm thinking of either running a pack of 30, or three packs of 10 nimh cells in series, in order to get ~36V. I would then use a rail splitter to get +/-18V and then regulate that to +/-15V. Charging the 3 12V packs seems like it would be easier, but I'm not sure if charging them in parallel with a 12V 1.9A charger would be safe.

I'd also like to know if this would offer similar performance to an elpac +/-15V 240mA regulated wallwart. Both the dac and amp run off of that power supply, so would the batter work as well?

Thanks for your help