Our battery has failed.
After 3 years of faithful service, our battery was accidentally allowed drain far below the acceptable minimum voltage for Li-ion cells, effectively ruining its capacity. In fact, it would be unsafe to recharge this battery in its present under-voltage state.
We will have to build a new battery. This is unfortunate, but since these cells lose 20% of their capacity per year in perfect storage conditions, it was inevitable.
This will push our schedule back a bit...