I've done a lot of work in the EV industry, usually "autonomia" is "range" when it refers to mileage on a single battery charge, but in this case, since it refers to time only, I'd use this.
Strange though, because surely the discharge time depends on load too?

anyway, this is rather clear:

http://www.sony-asia.com/productcontent/364394/productcatego...

this too:
http://www.chromausa.com/applications/electric-vehicle-batte...

2 hours of discharge time / of battery autonomy.
it could be either this or the above depending on the rest of the text.
These are BE synonims found in the following
UPS Technical Glossary - Uninterruptible Power Supplies Ltd

http://www.upspower.co.uk/ups-products/choosing-a-new-ups/up...
Autonomy. Also known as back up or discharge time, battery autonomy is a measure of the time for which the battery will support the critical load during a mains

Although all the other responses are also good, I think it is the equipment that is being run by a battery that is being described not the battery alone, am I correct? If you are describing a consumer appliance in a catalog, "run-time" or "runtime" would best describe the length of time a piece of equipment can run on the supplied power source and it has much better advertizing appeal than, say, "battery autonomy" which is a good literal translation but describes only the battery and not the product as a whole.