<s>
A	O
nickel	O
metal	O
hydride	O
battery	O
(	O
NiMH	O
or	O
Ni	O
–	O
MH	O
)	O
is	O
a	O
type	O
of	O
rechargeable	B-Architecture
battery	I-Architecture
.	O
</s>
<s>
However	O
,	O
the	O
negative	O
electrodes	O
use	O
a	O
hydrogen-absorbing	O
alloy	B-Application
instead	O
of	O
cadmium	O
.	O
</s>
<s>
They	O
are	O
typically	O
used	O
as	O
a	O
substitute	O
for	O
similarly	O
shaped	O
non-rechargeable	O
alkaline	B-Algorithm
batteries	I-Algorithm
,	O
as	O
they	O
feature	O
a	O
slightly	O
lower	O
but	O
generally	O
compatible	O
cell	O
voltage	O
,	O
and	O
are	O
less	O
prone	O
to	O
leaking	O
.	O
</s>
<s>
It	O
was	O
based	O
on	O
sintered	O
Ti2Ni+TiNi+x	O
alloys	B-Application
and	O
NiOOH	O
electrodes	O
.	O
</s>
<s>
The	O
batteries	O
 '	O
specific	O
energy	O
reached	O
50W·	O
h/kg	O
(	O
180kJ/kg	O
)	O
,	O
specific	O
power	O
up	O
to	O
1000W/kg	O
and	O
a	O
life	O
of	O
500	O
charge	B-Algorithm
cycles	I-Algorithm
(	O
at	O
100%	O
depth	B-Algorithm
of	I-Algorithm
discharge	I-Algorithm
)	O
.	O
</s>
<s>
Interest	O
grew	O
in	O
the	O
1970s	O
with	O
the	O
commercialisation	O
of	O
the	O
nickel	B-Algorithm
–	I-Algorithm
hydrogen	I-Algorithm
battery	I-Algorithm
for	O
satellite	O
applications	O
.	O
</s>
<s>
Research	O
carried	O
out	O
by	O
Philips	O
Laboratories	O
and	O
France	O
's	O
CNRS	O
developed	O
new	O
high-energy	O
hybrid	O
alloys	B-Application
incorporating	O
rare-earth	O
metals	O
for	O
the	O
negative	O
electrode	O
.	O
</s>
<s>
However	O
,	O
these	O
suffered	O
from	O
alloy	B-Application
instability	O
in	O
alkaline	O
electrolyte	O
and	O
consequently	O
insufficient	O
cycle	B-Algorithm
life	I-Algorithm
.	O
</s>
<s>
In	O
1987	O
,	O
Willems	O
and	O
Buschow	O
demonstrated	O
a	O
successful	O
battery	O
based	O
on	O
this	O
approach	O
(	O
using	O
a	O
mixture	O
of	O
La0.8Nd0.2Ni2.5Co2.4Si0.1	O
)	O
,	O
which	O
kept	O
84%	O
of	O
its	O
charge	O
capacity	O
after	O
4000	O
charge	O
–	O
discharge	O
cycles	B-Algorithm
.	O
</s>
<s>
More	O
economically	O
viable	O
alloys	B-Application
using	O
mischmetal	O
instead	O
of	O
lanthanum	O
were	O
soon	O
developed	O
.	O
</s>
<s>
In	O
1998	O
,	O
Ovonic	O
Battery	O
Co	O
.	O
improved	O
the	O
Ti	O
–	O
Ni	O
alloy	B-Application
structure	O
and	O
composition	O
and	O
patented	O
its	O
innovations	O
.	O
</s>
<s>
About	O
22%	O
of	O
portable	O
rechargeable	B-Architecture
batteries	I-Architecture
sold	O
in	O
Japan	O
in	O
2010	O
were	O
NiMH	O
.	O
</s>
<s>
This	O
percentage	O
has	O
fallen	O
over	O
time	O
due	O
to	O
the	O
increase	O
in	O
manufacture	O
of	O
lithium-ion	O
batteries	O
:	O
in	O
2000	O
,	O
almost	O
half	O
of	O
all	O
portable	O
rechargeable	B-Architecture
batteries	I-Architecture
sold	O
in	O
Japan	O
were	O
NiMH	O
.	O
</s>
<s>
The	O
most	O
common	O
is	O
AB5	O
,	O
where	O
A	O
is	O
a	O
rare-earth	O
mixture	O
of	O
lanthanum	O
,	O
cerium	O
,	O
neodymium	O
,	O
praseodymium	O
,	O
and	O
B	O
is	O
nickel	O
,	O
cobalt	B-Algorithm
,	O
manganese	O
,	O
or	O
aluminium	O
.	O
</s>
<s>
Some	O
cells	O
use	O
higher-capacity	O
negative	O
electrode	O
materials	O
based	O
on	O
AB2	O
compounds	O
,	O
where	O
A	O
is	O
titanium	O
or	O
vanadium	O
,	O
and	O
B	O
is	O
zirconium	O
or	O
nickel	O
,	O
modified	O
with	O
chromium	B-Language
,	O
cobalt	B-Algorithm
,	O
iron	O
,	O
or	O
manganese	O
.	O
</s>
<s>
When	O
fast-charging	O
,	O
it	O
is	O
advisable	O
to	O
charge	O
the	O
NiMH	O
cells	O
with	O
a	O
smart	O
battery	B-Application
charger	I-Application
to	O
avoid	O
overcharging	O
,	O
which	O
can	O
damage	O
cells	O
.	O
</s>
<s>
Some	O
chargers	O
do	O
this	O
after	O
the	O
charge	B-Algorithm
cycle	I-Algorithm
,	O
to	O
offset	O
natural	O
self-discharge	B-Algorithm
.	O
</s>
<s>
To	O
prevent	O
cell	O
damage	O
,	O
fast	O
chargers	O
must	O
terminate	O
their	O
charge	B-Algorithm
cycle	I-Algorithm
before	O
overcharging	O
occurs	O
.	O
</s>
<s>
A	O
method	O
for	O
very	O
rapid	O
charging	O
called	O
in-cell	B-Algorithm
charge	I-Algorithm
control	I-Algorithm
involves	O
an	O
internal	O
pressure	O
switch	O
in	O
the	O
cell	O
,	O
which	O
disconnects	O
the	O
charging	O
current	O
in	O
the	O
event	O
of	O
overpressure	O
.	O
</s>
<s>
Voltage	B-Algorithm
depression	I-Algorithm
(	O
often	O
mistakenly	O
attributed	O
to	O
the	O
memory	B-Algorithm
effect	I-Algorithm
)	O
from	O
repeated	O
partial	O
discharge	O
can	O
occur	O
,	O
but	O
is	O
reversible	O
with	O
a	O
few	O
full	O
discharge/charge	O
cycles	O
.	O
</s>
<s>
Under	O
a	O
light	O
load	O
(	O
0.5	O
amperes	O
)	O
,	O
the	O
starting	O
voltage	O
of	O
a	O
freshly	O
charged	O
AA	B-Algorithm
NiMH	O
cell	O
in	O
good	O
condition	O
is	O
about	O
1.4	O
volts	O
.	O
</s>
<s>
This	O
situation	O
can	O
occur	O
in	O
the	O
common	O
arrangement	O
of	O
four	O
AA	B-Algorithm
cells	I-Algorithm
in	O
series	O
in	O
a	O
digital	B-Device
camera	I-Device
,	O
where	O
one	O
cell	O
completely	O
discharges	O
before	O
the	O
others	O
due	O
to	O
small	O
differences	O
in	O
capacity	O
among	O
the	O
cells	O
.	O
</s>
<s>
Some	O
cameras	O
,	O
GPS	O
receivers	O
and	O
PDAs	B-Application
detect	O
the	O
safe	O
end-of-discharge	O
voltage	O
of	O
the	O
series	O
cells	O
and	O
perform	O
an	O
auto-shutdown	O
,	O
but	O
devices	O
such	O
as	O
flashlights	O
and	O
some	O
toys	O
do	O
not	O
.	O
</s>
<s>
Historically	O
,	O
NiMH	O
cells	O
have	O
had	O
a	O
somewhat	O
higher	O
self-discharge	B-Algorithm
rate	O
(	O
equivalent	O
to	O
internal	O
leakage	O
)	O
than	O
NiCd	O
cells	O
.	O
</s>
<s>
The	O
self-discharge	B-Algorithm
rate	O
varies	O
greatly	O
with	O
temperature	O
,	O
where	O
lower	O
storage	O
temperature	O
leads	O
to	O
slower	O
discharge	O
and	O
longer	O
battery	O
life	O
.	O
</s>
<s>
The	O
self-discharge	B-Algorithm
is	O
on	O
the	O
first	O
day	O
and	O
stabilizes	O
around	O
per	O
day	O
at	O
room	O
temperature	O
.	O
</s>
<s>
The	O
low	O
self-discharge	B-Algorithm
nickel	O
metal	O
hydride	O
battery	O
(	O
LSD	O
NiMH	O
)	O
has	O
a	O
significantly	O
lower	O
rate	O
of	O
self-discharge	B-Algorithm
.	O
</s>
<s>
These	O
cells	O
are	O
marketed	O
as	O
"	O
hybrid	O
"	O
,	O
"	O
ready-to-use	O
"	O
or	O
"	O
pre-charged	O
"	O
rechargeables	B-Architecture
.	O
</s>
<s>
The	O
self-discharge	B-Algorithm
rate	O
depends	O
upon	O
separator	O
thickness	O
;	O
thicker	O
separators	O
reduce	O
self-discharge	B-Algorithm
,	O
but	O
also	O
reduce	O
capacity	O
as	O
they	O
leave	O
less	O
space	O
for	O
active	O
components	O
,	O
and	O
thin	O
separators	O
lead	O
to	O
higher	O
self-discharge	B-Algorithm
.	O
</s>
<s>
Low-self-discharge	O
cells	O
have	O
somewhat	O
lower	O
capacity	O
than	O
otherwise	O
equivalent	O
NiMH	O
cells	O
because	O
of	O
the	O
larger	O
volume	O
of	O
the	O
separator	O
.	O
</s>
<s>
The	O
highest-capacity	O
low-self-discharge	O
AA	B-Algorithm
cells	I-Algorithm
have	O
2500mAh	O
capacity	O
,	O
compared	O
to	O
2700mAh	O
for	O
high-capacity	O
AA	B-Algorithm
NiMH	O
cells	O
.	O
</s>
<s>
corrosion	O
capabilities	O
)	O
,	O
and	O
addition	O
of	O
Al2(SO4 )	O
3	O
into	O
electrolyte	O
(	O
causing	O
reduction	O
in	O
MH	O
alloy	B-Application
corrosion	O
)	O
.	O
</s>
<s>
NiMH	O
cells	O
are	O
often	O
used	O
in	O
digital	B-Device
cameras	I-Device
and	O
other	O
high-drain	O
devices	O
,	O
where	O
over	O
the	O
duration	O
of	O
single-charge	O
use	O
they	O
outperform	O
primary	O
(	O
such	O
as	O
alkaline	O
)	O
batteries	O
.	O
</s>
<s>
Typical	O
alkaline	O
AA-size	O
batteries	O
,	O
which	O
offer	O
approximately	O
2600mAh	O
capacity	O
at	O
low	O
current	O
demand	O
(	O
25mA	O
)	O
,	O
provide	O
only	O
1300mAh	O
capacity	O
with	O
a	O
500mA	O
load	O
.	O
</s>
<s>
Digital	B-Device
cameras	I-Device
with	O
LCDs	O
and	O
flashlights	O
can	O
draw	O
over	O
1000mA	O
,	O
quickly	O
depleting	O
them	O
.	O
</s>
<s>
However	O
,	O
most	O
devices	O
compensate	O
for	O
the	O
voltage	O
drop	O
of	O
an	O
alkaline	B-Algorithm
battery	I-Algorithm
as	O
it	O
discharges	O
down	O
to	O
about	O
1volt	O
.	O
</s>
<s>
Thus	O
battery-level	O
indicators	O
designed	O
to	O
read	O
alkaline	B-Algorithm
cells	I-Algorithm
overstate	O
the	O
remaining	O
charge	O
when	O
used	O
with	O
NiMH	O
cells	O
,	O
as	O
the	O
voltage	O
of	O
alkaline	B-Algorithm
cells	I-Algorithm
decreases	O
steadily	O
during	O
most	O
of	O
the	O
discharge	O
cycle	O
.	O
</s>
<s>
They	O
also	O
produce	O
a	O
higher	O
voltage	O
(	O
3.2	O
–	O
3.7V	O
nominal	O
)	O
,	O
and	O
are	O
thus	O
not	O
a	O
drop-in	O
replacement	O
for	O
alkaline	B-Algorithm
batteries	I-Algorithm
without	O
circuitry	O
to	O
reduce	O
voltage	O
.	O
</s>
<s>
NiMH	O
batteries	O
have	O
replaced	O
NiCd	O
for	O
many	O
roles	O
,	O
notably	O
small	O
rechargeable	B-Architecture
batteries	I-Architecture
.	O
</s>
<s>
NiMH	O
batteries	O
are	O
commonly	O
available	O
in	O
AA	B-Algorithm
(	O
penlight-size	O
)	O
batteries	O
.	O
</s>
