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What is in your Hybrid battery? NiMh (Nickel-metal hydride) Basics

Pictured: Evergreen 28 Module Generation 2 Prius DIY pack, a single 7.2 volt module, Evergreen bus bars and nuts

Most customers are aware they have a high voltage battery of some sort in their hybrid vehicle. But did you know that your hybrid battery can comprise as many as 40 modules?

Below is a single NiMh (Nickel-metal hydride) module, containing 6 cells at 1.2 volts per cell - totaling 7.2 volts per module. A generation 2 or 3 Toyota Prius, Prius V, or Lexus CT200h has 28 modules, a Toyota Camry, Nissan Altima, or Lexus ES350h has 34 modules, and a Chevrolet Tahoe, GMC Yukon, or Cadillac Escalade has 40! 7.2 • 40 = 288 volts! This is why it’s extremely dangerous and potentially lethal when opening or disassembling any of the high voltage components in your hybrid vehicle and should never be attempted unless you are a trained L3 certified technician such as the ones we employ here at Evergreen Auto Solutions.

The Problem: Busbars and Corrosion

Corrosion is one of the biggest issues faced when dealing with a degraded or dying high voltage hybrid battery. The build up of corrosion leads to increased electrical resistance between the individual modules (cells) and their respective copper bus bar plates. The increase in resistance causes excessive heat as the electrical current passes through them, in turn burning out the bus bars with a cascading effect leading to varying voltage drops across the battery pack. This is one of several reasons your "Service Hybrid System" light or "Check engine" light will illuminate.

Pictured: Generation 1 Toyota Prius Hybird Battery with excessive corrosion buildup on busbars.

In the above picture you can see the terminal posts where the copper bus bars are fastened to the modules by stainless steel nuts, is excessively corroded. This condition is exacerbated by high temperatures usually stemming from poor cooling component performance, certain environmental conditions where the vehicle typically operates (salt water or road salt in colder climates) and excessive electrical resistance heating the terminal posts to a high degree as a result of improper torquing of the terminal nut, leading to an electrolyte leak at the terminal base.

The Solution: Evergreen Hybrid Battery Reconditioning

Pictured: Generation 2 Prius undergoing deep cycling and balance procedure after bus bar replacement.

As part of our Hybrid Battery Reconditioning service we replace each copper bus bar with brand new corrosion resistant nickel plated bus bars, as well as clean or replace their respective voltage sensors. Beyond the bus bar service we ensure the longevity of your battery pack by thoroughly cleaning and testing all the cooling components, eliminating every last bit of corrosion, deep cycling, and balancing to restore as much capacity as possible. All of this translates into the prolonged life of your hybrid battery, as well as increased fuel economy.

This is just one of the many procedures performed, as well as having your cooling components cleaned, tested, and every module fully charged and balanced.

Call or message us today for more information or to schedule an appointment.


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