There are numerous web sites which explain these batteries can fall into a sleep mode if left uncharged, but can be revived. However, lithium batteries are made with very reactive materials and if mishandled can explode and burn vigorously, emitting toxic gas. So I was reluctant to try charging the battery with other than the supplied charger. Ryobi Corded Leaf Blower & Vacuum, at Salvos Stores Leichhardt, for $50, which the couple were very happy with. But I thought I might as well get the cordless unit to work.
Please note that this is not an repair recommended for the inexperienced. Do not leave the battery charging unattended.