A user on the Dutch Prius forum reported giving a bad 12V battery to a mate who discovered half of the battery fluid had gone. So it might be worthwhile to check the fluid and top up with demineralized water if you feel your 12V battery is failing. I have a USB charger with a voltmeter and it is usually at 14.8V which is a bit above the gassing voltage.
If the battery is that low, it will not last long. You can fill it and use it until you can get another one. But carry a jumper with you. I speak from experience! Plus I've seen it in customer's cars. A few weeks maybe a month at most. It might last longer, but you are on borrowed time.
I keep seeing owners intent on converting their AGM batteries to flooded cell batteries instead. That eliminates the safety advantages of AGM. What is AGM Battery Technology?
