Got one if these, gives option of 20w on top slot or 45w (so 30w max charge for the battery) on the bottom slot.
https://www.amazon.co.uk/gp/product/B099S1FGC1/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1
In a rush, cook batteries on full charge - more chilled then use the 20w.
Works ok...