Prices range from $75 for the Commuter to $160 for the Trail https://www.knog.com.au/bike-lights/pwr-range.html. These use a proprietary power pack which is just the right size for being made from a single 18650 Li-ion battery. The spare power packs are $70 for a 3350 mAh for the PWR Bank Small to $90 for the PWR Bank Medium. If you compare that to the cost of buying a genuine Panasonic/NCR 3400 mAh battery for $10 or less, it makes carrying spare proprietary batteries pretty darn expensive. We are starting to see some bike lights that actually use a non-proprietary 18650 battery which would make a lot more sense than the Knog lights. Also, remember that Li-ion batteries recharge about 300 times before their output drops to 80% of the original value which makes using standard batteries an even better deal.