12v 20ah is 240 watt hour, a 5ah 7.4v lipo is 37 watt hour providing my maths is correct. the 20ah battery should be good for 15-17 AH useable capacity or around 200 watt hours so should be able to fully charge 5 5AH packs from flat or ten from half charged, plenty for the average days racing with one car. have a look around for a 40ah gel cell from an electric wheelchair, another cheap power source, a lot of companies fit new ones when servicing a chair even if there is nothing wrong with the old ones
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