NESC tech bulletin

National Aeronautics and Space Administration

www.nasa.gov

For information contact the NESC at www.nesc.nasa.gov

Applicability

All NiH

2 battery applications utilizing CPVs.

Background

The Wilkinson Microwave Anisotropy Probe (WMAP) was 

launched in 2001 and outfitted with an 11 cell CPV NiH

2

battery. WMAP was designed to operate in full sun conditions. 

An unexpected series of discrete voltage drops began in

August 2009 that were clearly traceable to the loss of one 

of the two individual cells contained within multiple battery 

CPVs. An examination of the limited telemetry available 

provided confirmation that each event was associated with a 

transient thermal load increase that occurred in conjunction 

with each step loss of voltage. Battery differential voltage 

telemetry indicated the events were apparently occurring 

randomly throughout the battery with no evidence that both 

cells within any given CPV were being affected. An NESC 

team was quickly assembled to evaluate the conditions and 

provide recommendations to arrest or reverse the degradation 

characteristics in order to complete the scheduled extended 

mission. 

Potential NiH

2 Battery CPV Issue

As a result of the investigation into the anomalous battery 

behavior, analysis and testing determined NiH

2 CPV battery 

cell designs are susceptible to a unique electrolyte bridging 

between the two internal cells that can potentially result in 

undesired ionic current flow, which can ultimately deplete 

the capacity within one of the two cells. The internal design 

configuration of a normal CPV allows free material transport 

between cells as both cells within a CPV are intended to 

share the hydrogen gas necessary for NiH

2 cell functionality. 

Two conditions were identified where it is possible for free 

potassium hydroxide (KOH) electrolyte to creep between the 

cell stacks and to establish an undesirable conductive ionic 

pathway that effectively shorts out one of the two cells within 

the CPV. Those conditions are: 1) activating the NiH

2 CPV 

cells with excess electrolyte present or 2) allowing the cells 

to reach very low states of charge during operation. Based on 

observations and available data, once the electrolyte bridge 

is established there are no effective means to eliminate the 

problem with the possible exception of fully reconditioning the 

battery cell, or at least extended operation (up to a few weeks) 

in an open circuit condition. The application of periodic high 

rate charge pulses (between C/10 and C/4) was observed to 

be effective in at least temporarily stemming the continued 

voltage degradation of the WMAP battery and in a similar 

laboratory test battery. However, careful consideration to 

avoid high temperatures (above +10°C) needed to be in place 

to reduce the possibility of thermal runaway. 

References

Wilkinson Microwave Anisotropy Probe (WMAP) Battery

Operations Problem Resolution Team (PRT), NESC Document 

Number: RP-10-00608, NASA TM Number: TM-2010-216840

Effects of a Simulated Electrolyte Bridge in a Common

Pressure Vessel (CPV) Nickel Hydrogen Cell, Aerospace Report 

Number: ATR-2010 (5175)-1

Porous 

wall wick

Plastic septum, 0.05” thick

Weld ring

Weld ring

Core, end plate, 

weld ring detail

Core

Core

Center wall of 

core, 0.1” thick

Tig weld of 

common leads

(+) Lead bundle, Ni

Plastic

Inconel

Electrolyte 

bridge

Lower

stack

Upper

stack

Lower stack

Upper stack

Upper stack end plate

Upper stack end plate

Upper stack end plate

Lower stack end plate

Lower stack end plate

Lower stack end plate

Lower

stack 

Upper

stack

(–) Lead bundle, Ni

•••

•

•

•

•••

•••

•

•

•

•••

•

•••••••

•

0.4”

••

••

•

Simple Illustration of Ni-H2 Common Pressure Vessel Design and 

Identified Possible Electrolyte Bridging Locations

NASA Engineering and Safety Center Technical Bulletin No. 11-01

Nickel-Hydrogen (NiH

2) Common Pressure Vessel (CPV) Cell

Capacity Loss and Voltage Collapse 

During an investigation of anomalous voltages during a NASA scientific mission, a NASA Engineering and 

Safety Center (NESC) team discovered that the design of NiH

2 CPV batteries may be susceptible to a unique 

electrolyte bridging between the two internal cells resulting in undesired ionic current flow. This condition 

can lead to depletion of the capacity within one of the two cells.