2008 Prius All warning lights are on.

I believe that what you may be thinking of is this; with your HV safety gloves on, remove the orange service plug and the metal upper battery case. Using a CAT III rated DVOM, test for any voltage between one of the battery pack busbars and chassis ground- there should be zero volts. Any voltage reading indicates some kind of leakage. Sometimes there is obvious electrolyte spillage, sometimes there is external "burning" evident on the module shell. I have read about cracks in the plastic shell around the bottom mounting bolt insert.
I have never tried using megger on a HV battery.

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Just for others coming upon this thread, that is not the the ABS unit that is the brake control power supply.

 

Like any ohmmeter, a megger won't give you a meaningful reading if applied to something that's a voltage source, like a battery. It can be used to check the isolation of all the other components (wiring, relays, etc.) that are inside the battery enclosure, but are not themselves voltage sources. Such checks should done with the parts in question properly disconnected or isolated from voltage sources, which won't be news to anyone with training on using a megger.

Using a high-impedance voltmeter between terminals of the battery and body ground can be a way of detecting a leak from a battery module. Even better, if done early enough that there is likely to be only one leak, it can give you a good idea of where in the stack of modules the leak might be. For example, the battery is about 201 volts 'wide', so if the voltage you measure from one end of it to body ground looks like, say, 90 volts, you might look for a leak around the 12th or 13th module from that end.

The lower the impedance of the voltmeter, the less reliable that technique may be (it will bias the displayed voltage lower and make the leak appear 'closer' to the end you're measuring from), but you can mitigate that effect by repeating the measurement from the other end of the battery.

If the battery has been throwing leakage codes long enough that by now it's likely to have more than one leakage path, then the technique isn't as useful. The meter will still show some voltage reading, but it will just be the Thévenin-equivalent voltage for the battery, the multiple leakage paths present, and the meter's impedance, and there won't be any easy interpretation of it as a physical location of a single leak.

 

Interesting
Any specific locations on hatch to inspect periodically?

 

Sure. Use the search function on the Gen2 forum for "hatchback water leak" and you'll get lots of info.

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