I turned off my nexus 7 last night with about 30% battery. This morning I turned it on to discover that it had only charged to 50%. Today I charged it while it was on with about 35% battery. A few hours later it was only at 62%.
Are you using the stock charger? Battery Graph from Playstore (free) will help you follow charging/discharging cycles. Gauge Battery is useful in assessing battery status.