How many amps do you need? What capacity do you need? 53 volt is meaningless by itself.
53 volt (51.8V for 14 cell, 55.5 for 15 cell) is potential lethal if you use good enough packs. So be very careful. Easiest way would be to buy 3 5s1p packs for 55.5v.
http://www.flightpower.co.uk/index.asp?currency=GBP&page=Products/index.asp^currency=GBP
Three of those, won't be too cheap. At 25C that's a good 55 amps though, only 2.17Ah though.
http://www.flightpower.co.uk/index.asp?currency=GBP&page=Products/index.asp^currency=GBP
Three of these would allow 83 amps worth of juice, and 3.3Ah.
http://www.flightpower.co.uk/index.asp?currency=GBP&page=Products/index.asp^currency=GBP
Feeling rich? 125 amps, tonnes of juice! 5Ah too.
If you don't need this kind of current, you can do for smaller lower C packs and save money and weight.
http://www.giantcod.co.uk/product_in...55906aef91ee6f
No idea on the quality of this, but 15C will mean 69 amps and 4.6Ah is reasonable.
But anyway, without your requirements it's like asking how long is a piece of string?