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 4 Fixed typos and grammar edited Apr 15 at 17:14 ndemou 13344 bronze badges Rules of thumb given in other answers are often good enough but if you can find the datasheet of the battery it's best to check the relevant graph. As an example here's the datasheet of a low cost 12V battery. In the datasheet you'll find this graph: Let's say that this is a 7Ahr battery. 1C means discharging with a constant current of 7Amp. Let's also say7Ahr capacity and that you want to draw 14A from that battery. So you'llYou'll have to observe the 2C curve where you'll(2C means to discharge at 7Ahr*2/h=14A). You'll note that this battery and is discharged by drawing 14Amp will drop to 9.5V-10V after about 15mins. OfcourseOf-course this is true only true for a fresh from the shelf battery kept at 25 deg.Celsius. Temperature, age and usage negatively affect itsthe performance. Rules of thumb given in other answers are often good enough but if you can find the datasheet of the battery it's best to check the relevant graph. As an example here's the datasheet of a low cost 12V battery. In the datasheet you'll find this graph: Let's say that this is a 7Ahr battery. 1C means discharging with a constant current of 7Amp. Let's also say you want to draw 14A from that battery. So you'll have to observe the 2C curve where you'll note that this battery and is discharged by drawing 14Amp will drop to 9.5V-10V after about 15mins. Ofcourse this is true only for a fresh battery kept at 25 deg.Celsius. Temperature, age and usage negatively affect its performance. Rules of thumb given in other answers are often good enough but if you can find the datasheet of the battery it's best to check the relevant graph. As an example here's the datasheet of a low cost 12V battery. In the datasheet you'll find this graph: Let's say that this is a battery with 7Ahr capacity and that you want to draw 14A. You'll have to observe the 2C curve (2C means to discharge at 7Ahr*2/h=14A). You'll note that this battery will drop to 9.5V-10V after about 15mins. Of-course this is only true for a fresh from the shelf battery kept at 25 deg.Celsius. Temperature, age and usage negatively affect the performance. 3 added 405 characters in body edited Apr 15 at 16:46 ndemou 13344 bronze badges Rules of thumb given in other answers are often good enough but if you can find the datasheet of the battery it's best to check the relevant graph. As an example Here's onehere's the datasheet fromof a low cost 12V battery. In the datasheet you'll find this graph: If the batteryLet's say that this is rated ata 7Ahr thenbattery. 1C means discharging with a constant current of 7Amp. Let's also say you want to draw 14A from that battery. So you'll have to observe the 2C curve where you'll note that this battery and is discharged by drawing 14Amp will drop to 9.5V-10V after about 15mins. Ofcourse this is true only for a fresh battery kept at 25 deg.Celsius. Temperature, age and usage negatively affect its performance. Rules of thumb given in other answers are often good enough but if you can find the datasheet of the battery it's best to check the relevant graph. Here's one from a low cost 12V battery: If the battery is rated at 7Ahr then 1C means discharging with a constant current of 7Amp. Rules of thumb given in other answers are often good enough but if you can find the datasheet of the battery it's best to check the relevant graph. As an example here's the datasheet of a low cost 12V battery. In the datasheet you'll find this graph: Let's say that this is a 7Ahr battery. 1C means discharging with a constant current of 7Amp. Let's also say you want to draw 14A from that battery. So you'll have to observe the 2C curve where you'll note that this battery and is discharged by drawing 14Amp will drop to 9.5V-10V after about 15mins. Ofcourse this is true only for a fresh battery kept at 25 deg.Celsius. Temperature, age and usage negatively affect its performance. 2 added link to datasheet from which image was taken edited Apr 15 at 16:30 ndemou 13344 bronze badges Rules of thumb given in other answers are often good enough but if you can find the datasheet of the battery it's best to check the relevant graph. Here's oneHere's one from a low cost 12V battery: If the battery is rated at 7Ahr then 1C means discharging with a constant current of 7Amp. Rules of thumb given in other answers are often good enough but if you can find the datasheet of the battery it's best to check the relevant graph. Here's one from a low cost 12V battery: If the battery is rated at 7Ahr then 1C means discharging with a constant current of 7Amp. Rules of thumb given in other answers are often good enough but if you can find the datasheet of the battery it's best to check the relevant graph. Here's one from a low cost 12V battery: If the battery is rated at 7Ahr then 1C means discharging with a constant current of 7Amp. 1 answered Apr 15 at 15:39 ndemou 13344 bronze badges