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NiMH Battery Specifications

Batteries may have different characteristics and specifications (specs), e.g.: Chemistry, Nominal (or Design) Capacity, Full Charge Capacity (FCC), Remaining Capacity, Nominal Voltage, Open Circuit Voltage (OCV), Internal Resistance, Self-Discharge Rate, Number of Recharge Cycles, Life Span, Internal Protective Valves or Electrical Switches, Mechanisms, Weight, Size, Output Power, Energy Density, Material of Enclosure, Type of External Connectors, etc, just few to mention. Our Glossary Page explains some of those terms.

The code on every battery contains information about manufacture date. It is not that hard to verify how “brand new” the batteries are.

Watch Video: Battery Modules Manufacture Date Scan: Original, Swapped or Rebuild?

The most important thing though is to check their current state of health.

Prismatic Batteries taken from the hybrid car are not designed to work without physically being compressed from the sides. Their side panels may not withstand the pressure formed inside while charging. If you try to charge individual battery without it being properly handled – it will bulge and may even blow!
Batteries could have chemically hazardous substances inside them and normally should have relevant markings. Please always look for those if you intend to experiment.
Batteries in the hybrid car are normally assembled in series forming hazardous high voltage!
For example:
  • Toyota Prius NHW-11 Battery Pack uses 38 prismatic plastic batteries. At 8.4 volts each that would present the high voltage inside the pack: 38 x 8.4 = 319.2 V!
  • Toyota Toyota Prius NHW-20 Battery Pack uses 28 prismatic batteries. 28 x 8.4 = 235.2 V!

In real life NiMH Battery in Toyota Prius (NHW-11 & NHW-20) operates between 7.2 and 8.4 Volts with the minimum and maximum allowed values being 6V and 11.5V respectively.

Modern NiMH Batteries used in Toyota Prius, Camry and Lexus Hybrids are manufactured by Primearth EV Energy (PEVE).

Battery Specifications:

  • Nominal Voltage: 7.2V
  • Nominal Capacity: 6.5Ah
  • Weight: 1.04kg
  • Dimensions (mm): 19.6(W)×106(H)×285(L)
NHW-20 Battery - NP2 Modules

NHW-20 Battery – NP2 Modules

OCV of that individual battery on the photo above is 7,96V which is normal. We have tested that pack in 2012 and FCC was around 4,8Ah which is OK considering it was from the 4 year old (year 2008) wrecked Prius.

One government supported specialised Lab in USA runs standardised capacity tests on battery packs in controlled environment – i.e. from sample set of cars when those are new and on the same set of cars after 160000 miles. Here are some of their results clearly showing that batteries even when new could show capacity below designed and they degrade and loose their capacity even more with age and number of cycles:

Official US Lab Battery Degradation Test Results

Official US Lab Battery Degradation Test Results

Prismatic battery modules used in Prius NHW-11 are little bit different in design and size from those used in NHW-20, see photo below:

NHW-11_Battery Module NP1

NHW-11_Battery Module NP1

EV Energy web site as of December 2013 no longer displays information about the plastic prismatic battery for the second generation Prius. The relevant page was there in March 2013. In November 2013 it was no longer there. Looks like production for those by EV Energy has stopped.

 Newer modules from NHW-20 can be used to successfully re-assemble the NHW-11 packs.

To do such refurbishment of the battery pack individual batteries should have their characteristics being matched, e.g. full charge capacity should be the same. Batteries from NHW-11 and NHW-20 models should not be mixed. Ideally donor batteries from couple of NHW-20 packs with the same FCC could do the job. The tricky part is to measure FCC quickly and efficiently.
That is where our High Voltage Battery Testing Complex does the job!

Prius NHW-10 cylinder type batteries sometimes called “bamboo sticks”. Some of their characteristics are similar to Prismatic Batteries – e.g. nominal capacity and voltage.

NHW-10 Battery (aka Bamboo_Stick)

NHW-10 Battery (aka Bamboo_Stick)

Some enthusiasts dismantle old “bamboo sticks”, select good cells and rebuild the stick using spot welding machine.

It is possible for our High Voltage Battery Testing Complex to measure individual cells if you make special cradle to contact with individual cells in “Bamboo Stick”.