If you purchase a backpack from the UK, then you will have a warranty of some sorts.
I purchased one last September for £215 (all in including postage and packaging) from Williamson Pumps.
Six months later and after a hard Winter my battery stopped working. I phoned Williamson Pumps and the battery wasn't covered in the warranty. In fact they didn't have any at that moment and I would have to wait for them to order some in.
After a 'safari', I got another two similar batteries for £5.00 each from a local car shop! So no big cheese.
I've also recently purchased a back pack from E-Bay (USA) for £170 in total.
My original backpack is still going strong, but I wanted a spare, just in case.
They're robust bits of kit and if one lasts me at least a year, I'm happy with that.