1) I leave it on charge permanently as it suggests - I use it regularly and it has never run down fully so I don't know.
2) Cannot be used with spills of liquid to the best of my knowledge
It is very powerful for general use around the home, getting in crevices, removing cobwebs, on stairs in car etc when you often don't want to get big vacuum cleaner out.
It's difficult to tell when the batteries are fully charged since the charging lamp stays on as long as it's in the docking unit. If the batteries are completely flat I would recommend at least 12 hours on charge. Yes it will clean a car, just, but I found that, as Which? magazine stated, it will run for about 9 minutes at full speed before switching off.
We have not actually run the vacuum long enough to run tne battery down. This cleaner is somewhat heavier than our 12v version - probably due to the greater capacity battery. What is clear though, is that the battery does maintain it's power throughout usage rather than gradually reducing as is the case with the lesser model.
The longest we have used the vacuum for is around 15 minutes and it continued as well as it was when first switched on. We are still as delighted with this versatile vacuum cleaner as we were when first we purchased it. If there is a very minor niggle, it is that removing and cleaning the filter takes a little getting used to. The on/off switch was rather stiff but a short squirt of WD40 sorted it out.
Our opinion is that if you have a requirement for a rechargeable vacuum cleaner, buy this one.