Glad your issue is resolved. However, I just want to educate you (and anyone else who stumbles on this).
so, plenty of time to charge a low battery
It's a common misconception that an alternator in a car can charge a low battery, but this is incorrect. The old generators would, but an alternator will not charge a drastically low battery. The generators ...
Is it safe to jump a battery that low: not really. Make that not at all safe
A healthy battery is about 12.8V
by the time it hits 11V, it is massively discharged already.
To get to 3.6v, you battery is so discharged that you have already damaged it. Or much more
likely, it has already been damaged, causing this voltage.
If you jumpstart it, several things ...