Jump starting our dead Prius

Overcharging like that is a good way to ruin a battery.

 

Good point on constant current VS constant voltage. I suspected something of the sort. As Ed the fox stated, his typical reading is about 12.3 Volts, the same with me, regardless of the type of 12V I am using.

 

The charger I use starts at 3ah and gradually decreases to between 0 - 1 amp charge rate. I believe, and the EEs will correct me, but as the charge improves on the battery ( when bench charging ) the internal resistance to this charging current increases as the voltage on the battery improves til essentially equalibrium is reached and slight current continues to flow and keep the battery in a optimum state. Naturally one does not hook up a montrous charger to a small Prius battery. So there is no fear of overcharging! Common sense and feeling the walls of the battery for overheating, or low water (not Prius) is also good practice. PS I have never ruined a battery.

 

As vertex stated, a proper 3-stage charge algorithm will not overcharge, but some standard "dumb" hardware-store type chargers are a constant voltage with current limited by the transformer and a thermal cut-out. I've seen the voltage as high as 18 volts (open circuit) on these, so could easily overcharge and vent the small Prius battery.

The Vector/Black & Decker models are relatively inexpensive units with a true 3-stage charge.

I just put a Optima in another Prius yesterday. It's owner had been carrying around a portable jump box for cold morning starts. Takes under 10 minutes even if you drop a screw down in the battery well! =)

 

Great info. Got a dead battery. I jumped it to get it going.
Once at home I put a trickle charge on. I hooked the charger at the
post under the hood. Not at the battery. Is this ok?

 

Yes