Nybble seems to work fine most of the time with Nitecore IMR14500 Li-ion 3.7V 650mAh, pulse discharge 6.5A. Available in UK nitecore.co.uk and in Australia at https://www.mymultitools.com.au/nitecore-imr14500-3-7v-battery-650mah.html and https://www.liteshop.com.au/content/nitecore-650mah-imr-14500-high-drain-rechargeable-battery-ni14500a/