Nikon states for the D610:
An efficient power circuit, the highly energy-efficient EXPEED 3 and other features reduce the power consumption of the D610. It adopts the EN-EL15 Rechargeable Li-ion Battery, which is the same as the D800 series and D7000. It is possible to shoot approx. 900 shots* of still images on one charge of the EN-EL15 Rechargeable Li-ion Battery loaded in the camera body. As power sources, one EN-EL15, EH-5b AC Adapter (with EP-5B Power Connector) and MB-D14 Multi-Power Battery Pack can be used.
So your 250 images for 13% is exceptionally good,,,Why it would use juice while in stand by,,, don't use standby or get a grip