A balanced energy budget is the key element in an animal’s ability to survive and reproduce. Accurately understanding this budget, called the field metabolic rate (FMR), throughout an annual cycle is a very difficult challenge. Typically, previous estimates for bats have been accurate to +/- 50%. A practical method for calculation of FMR for bats to a high level of accuracy is possible using a model based on physiology and quasi-steady aerodynamics. The fidelity of this modelling approach has been cross-checked using twenty three empirical data measurements using doubly labelled water methods published for fifteen Old and New World species. Predictions have been made for adult bats in non-reproductive, pregnant and lactating conditions. Predictions were generally within 5% of the empirical values for non-reproductive adult bats and pregnant females (average 4.4%, sd 5.6%, n = 19). Predictions with errors over 10% were limited to lactating females from one of four species where the timing of the collection of the empirical data may have been a contributing factor. Calculation of metabolic power at these improved accuracies can provide inter-species level energy budget assessments for bats in guilds, communities and also at a continental level.