This section deals with repairs to the 280V HV NMIH Battery Pack contained behind the rear seats in the Prius NHW10. None of the information here applies to any other vehicle or battery pack.


Caution / PrecautionsEdit

Voltages, chemicals and chemical reactions inside the HV battery pack of the Prius can be lethal in many ways. Repairs to the pack must be done with as much care as defusing a bomb as it could cost you your life. If you are not at all comfortable performing these repairs, do not have the mandatory safety equipment, know-how, mental clarity, alertness, caution and a healthy respect for the powers contained within - DO NOT TOUCH THE HV BATTERY PACK!

Some things to keep in mind:

  • DC Voltages are lethal even at lower voltages!
  • Even unused battery packs contain lethal voltages. Do not think that if your car or pack has been sitting unused for years, it is totally harmless. Infact, corrosion, cracks and water that may have entered the pack over the years will make it MORE dangerous.
  • Never operate the pack with the cover removed! DO NOT DO IT!
  • Always remove the orange rear isolation plug before touching the battery! This plug connects two battery half-packs contained inside and effectively halves the total voltage present inside the battery. If you cannot or do not know how to remove the plug, DO NOT TOUCH THE BATTERY.
  • Shorted or overcharged NMIH battery sticks and cells will EXPLODE, LEAK and/or catch fire! These are not the same NMIH batteries that you might find in a remote control car! They can deliver well over 10A of current and will reach high temperatures very very quickly if overcharged, shorted or abused! If charging the sticks/cells outside of the battery, use a proper NMIH charger with current limiting.

Be safe:

  • Wear electrical isolating gloves.
  • Wear a tough pair of safety goggles.
  • Do not work alone, have a buddy nearby that can help if you get zapped.
  • Be careful with metal wrenches/screwdrivers and etc. Wrap them up in isolating electrical tape if possible to avoid accidentally shorting wires, contacts and terminals inside the battery.
  • Use magnetised screwdrivers and etc. Be careful not to drop screws inside the battery pack.
  • Have plenty of light.
  • Plan and think twice before each step to avoid disaster.

Pack removalEdit

1) Remove the back carpet walls from the boot


2) Disconnect the 12v aux battery

3) Pull out (rotate 90degrees) and then pull off, and totally remove the HV isolation orange leaver/circuit breaker and place it in your tool box for safety. This breaks the HV circuit.


4) Remove the HV boot charger


5) Remove the left-hand support plate covering the vents by removing 4x 10mm bolts.

6) Unplug the top vent tube from the HV battery pack.

7) Remove the diversion flap box by unbolting 2 x 10mm bolts and then just pulling it out and disconnecting the power plug.

8) Unplug remaining 12v connectors

9) Remove 4x 12mm bolts from the bottom of the HV battery pack inside in the back seat area, now remove the back seat base by pulling it upwards at the leading edge, both ends, then pull the seat base out.


10) Remove the headrests and unbolt the middle seatbelt 14mm bolt and place on the back parcel shelf.

11) Unbolt 3x 10mm bolts at the bottom of the rear seat backrest and remove it by pulling upwards and holding the outer seatbelts clear.

12) Remove the air intake duck by removing 2 x 10mm bolts and 1x screw.


13) Remove all the main 10 x 12mm bolts that are holding in the HV battery pack at the top and bottom.

14) Pull the HV battery pack forward by lifting a little and then un plug the 2x main orange HV connections at the end.


15) You can now lift out the HV battery pack with a forklift as it is 88kg.


16) [Optional] Remove the metal fascia plate by removing the 10mm ring of bolts and 12mm nuts and push 2 screwdrivers (the circuit breaker removed in step 3 can all be used) into the top safety interlink and then this will release it to allow the plate to come off.

It's also possible to drop the HV battery pack (after first removing the fascia plate) into laying down in the boot and then dissembling it in the boot and removing the half packs but it might be hard work.

HV Battery Disassembly - Removing the Half-PacksEdit


Required tools: 10mm socket and ratchet with an extension bar of about 6"-8" and a x screwdriver and a small crowbar.

1) Remove the ECU (the metal unit on the LHS) and unplug all connections.

2) Remove the plastic fan in the centre for the battery box, not forgetting to carefully pull out the air intake thermal and pull through the motor rubber breather tubes at the bottom as well.

2) Remove the distribution board cover on RHS.

3) Unbolt all the main cable bolts from the distribution board and then remove the boards own retaining nuts and bolts and bull the board off completly disconnecting any low volt connections.

4) Lay the case on its back and remove 4 x bolts from underneath holding in the backs of the half packs.

5) Sit the pack up right again and remove 4 x bolts at the front of the base of the half packs.NB: the "earth strap" is on the left hand end bolt to provide earth for the ECU. Failure to replace it on rebuild will result in your fan going backwards due to the earthing fault.

6)  Now you are ready to remove 2 x half packs. To do this use the crowbar and gently lever the packs up and forward, starting with the right hand 1 first.  a 10mm socket to remove the end connections.

7) Disconnect the interconnecting top cable .

Half Pack Disassembly Edit

Remove the orange end plate that does NOT have the 4x corner bolts. this the gives you access to the thermal connections. Use a 10mm socket and wrench to remove the bolts, and a battery drill/driver set to the lowest torque setting, to remove all the screws. The other plate (With the 4x corner bolts) can be left in place when removing/replacing battery sticks.