The good news is that you do not have to replace the complete battery in your Prius if only a few cells have failed. The photo shows the inner array of the main battery. Two cells were defective which we sourced and replaced. Obviously corrosion had formed on all the connecting terminals. The corrosion was methodically cleaned off each bolt connector washer and nut before re assembling.


Connect computer, Read errors, Read live data, Enter work bay Set up safe working area, Remove boot contents to access auxiliary battery and High voltage battery fuse Test high voltage gloves for leaks, Wear high voltage gloves Access and remove circuit breaker, Test Auxiliary battery Remove all boot trims Remove rear seats Remove rear battery case grounds and covers,  Remove cover for isolating relays, Remove wiring connectors to relays, Remove battery mount bolts Toyota Model Prius Odometer 161157 , Remove battery assembly, Dismantle battery covers Inspected battery , wiring and computers Battery terminals were badly corroded, Removed all nuts and bridging washers on both sides of the battery pack, Soaked nuts and bridges in bicarb solution, Cleaned terminals on individual battery blocks, Measured voltage on each block isolated from each other, Cleaned corrosion and insects from relay and computer housings, Remove plugs to computers Coated in contact anti corrosion fluid, Refit connectors, Remove batteries hold clamps, Remove batteries Replace faulty individual batteries , temperature sensors, Cleaned corrosion from sensors, Remove cooling fan assembly from driver rear seat base, Fan was blocked, Clean fan ducts and Clean fan blades, Test fan operation Reassemble battery pack Refit cleaned bridge washers and nuts Reassemble covers Refit high voltage battery to vehicle Reassemble rear trims Reconnect circuit breaker Reconnect auxiliary battery Test operation Carry out health check