Gen II Battery holding charge

The battery side might be showing some voltage due to an electrolyte leak in a module or two. This is why Toyota's service procedure requires the use of insulating gloves when working on the traction battery.

If you don't have such gloves, at minimum you want to be using only one hand when contacting the battery interior (to avoid having high voltage pass through your heart.) Once you disconnect and remove one of the orange bus bars that provide a series connection to the modules, the battery can be deemed safe. Until that point, it can still inflict significant damage upon you.

 

Don't worry about it. Just work on the battery, observing the safety precautions I suggested.

 

Don't bother with that, just double up a set of rubber dish gloves while you undo the HV cables from the pack (assuming the 12V aux battery was already disconnected and orange traction battery safety plug was also removed), then unplug the main battery cables from the hybrid relay. After that you can remove the pack from the truck and you shouldn't need the gloves anymore (check voltage just to be sure).

 

If you really want to find the bad cells, don't just go by voltage, you need to load test them somehow. Example, I bought a cell to replace a bad one in my pack, which was obviously bad.6.4 volts. I got a used one off Ebay with real high voltage reading. Well after driving around for a week, there goes the lights again. So I made a load tester from a a 100amp load tester I had for regular car batteries. I clipped one of the two elements to make it more like a 50amp tester. Then I went down every cell for 20seconds on the load, and with my multimeter connected to measure the voltage drops when I hit the load. Well wouldn't you know ,the cell with the highest voltage, dropped like a rock when I flipped the load on it. HAd the highest resistance. It was the cell I bought off Ebay to replace the original bad cell First time the code told me it was module 13, second time it told me it was block 10, both times it was wrong, it was the same cell, and it was block 14. So much for the cars diagnosis. I got it running fine after recycle balancing the cells, and placing by order of resistance and capacities, but not before a ordered a 2012 HV batt. out of a wrecked car. I cycled those cells too, and eventually put them in my 2005 HV case. I'm going to be selling most of my 05 cells, and keeping a few for spares when I get a chance. I found interesting, some of my 05 cells had better capacities than the 2012 cells did, now maybe I should of measured all 56, and just used the strongest cells, but I don't care, I running along fine, and drowning in spare cells.lol My wife is freaking out with all this mess of chargers,batteries,meters everywhere. I told her this is what you have to get used to when you own Hybrids, and she has a 2013 herself.

 

Principle is the same, but the load tester doesn't need to be very sophisticated or powerful, see here:

Gen II Prius Individual Battery Module Replacement | Page 13 | PriusChat

Obviously the message here is to rebuild properly you need to do both load and capacity testing.

 

Agree, just need a known load to apply equally to each one to take some readings.