<s>
A	O
backup	B-Algorithm
battery	I-Algorithm
provides	O
power	O
to	O
a	O
system	O
when	O
the	O
primary	O
source	O
of	O
power	O
is	O
unavailable	O
.	O
</s>
<s>
Backup	B-Algorithm
batteries	I-Algorithm
range	O
from	O
small	O
single	O
cells	O
to	O
retain	O
clock	O
time	O
and	O
date	O
in	O
computers	O
,	O
up	O
to	O
large	O
battery	O
room	O
facilities	O
that	O
power	O
uninterruptible	O
power	O
supply	O
systems	O
for	O
large	O
data	O
centers	O
.	O
</s>
<s>
Small	O
backup	B-Algorithm
batteries	I-Algorithm
may	O
be	O
primary	B-Algorithm
cells	I-Algorithm
;	O
rechargeable	O
backup	B-Algorithm
batteries	I-Algorithm
are	O
kept	O
charged	O
by	O
the	O
prime	O
power	O
supply	O
.	O
</s>
<s>
Backup	B-Algorithm
batteries	I-Algorithm
in	O
aircraft	O
keep	O
essential	O
instruments	O
and	O
devices	O
running	O
in	O
the	O
event	O
of	O
an	O
engine	O
power	O
failure	O
.	O
</s>
<s>
Each	O
aircraft	O
has	O
enough	O
power	O
in	O
the	O
backup	B-Algorithm
batteries	I-Algorithm
to	O
facilitate	O
a	O
safe	O
landing	O
.	O
</s>
<s>
Large	O
aircraft	O
may	O
have	O
a	O
ram	B-Algorithm
air	I-Algorithm
turbine	I-Algorithm
to	O
provide	O
additional	O
power	O
during	O
engine	O
failures	O
.	O
</s>
<s>
Backup	B-Algorithm
batteries	I-Algorithm
are	O
almost	O
always	O
used	O
in	O
burglar	O
alarms	O
.	O
</s>
<s>
The	O
backup	B-Algorithm
battery	I-Algorithm
prevents	O
the	O
burglar	O
from	O
disabling	O
the	O
alarm	O
by	O
turning	O
off	O
power	O
to	O
the	O
building	O
.	O
</s>
<s>
The	O
backup	B-Algorithm
battery	I-Algorithm
usually	O
has	O
a	O
lifespan	O
of	O
3-10	O
years	O
depending	O
on	O
the	O
make	O
and	O
model	O
,	O
and	O
so	O
if	O
the	O
battery	O
runs	O
flat	O
,	O
there	O
is	O
only	O
one	O
main	O
source	O
of	O
power	O
to	O
the	O
whole	O
system	O
which	O
is	O
the	O
mains	O
power	O
.	O
</s>
<s>
Should	O
this	O
fail	O
as	O
well	O
(	O
for	O
example	O
,	O
a	O
power	O
cut	O
)	O
,	O
it	O
usually	O
triggers	O
a	O
third	O
backup	B-Algorithm
battery	I-Algorithm
located	O
in	O
the	O
bellboxes	O
on	O
the	O
outside	O
of	O
the	O
building	O
which	O
simply	O
triggers	O
the	O
bell	O
or	O
siren	O
.	O
</s>
<s>
Modern	O
personal	O
computer	B-Device
motherboards	I-Device
have	O
a	O
backup	B-Algorithm
battery	I-Algorithm
to	O
run	O
the	O
real-time	O
clock	O
circuit	O
and	O
retain	O
configuration	O
memory	O
while	O
the	O
system	O
is	O
turned	O
off	O
.	O
</s>
<s>
This	O
is	O
often	O
called	O
the	O
CMOS	O
battery	O
or	O
BIOS	B-Operating_System
battery	O
.	O
</s>
<s>
The	O
original	O
IBM	B-Operating_System
AT	I-Operating_System
through	O
to	O
the	O
PS/2	B-Device
range	O
,	O
used	O
a	O
relatively	O
large	O
primary	O
lithium	O
battery	O
,	O
compared	O
to	O
later	O
models	O
,	O
to	O
retain	O
the	O
clock	O
and	O
configuration	O
memory	O
.	O
</s>
<s>
These	O
early	O
machines	O
required	O
the	O
backup	B-Algorithm
battery	I-Algorithm
to	O
be	O
replaced	O
periodically	O
due	O
to	O
the	O
relatively	O
large	O
power	O
consumption	O
.	O
</s>
<s>
Modern	O
systems	O
use	O
a	O
coin	O
style	O
primary	B-Algorithm
battery	I-Algorithm
.	O
</s>
<s>
In	O
these	O
later	O
machines	O
,	O
the	O
current	O
draw	O
is	O
almost	O
negligible	O
and	O
the	O
primary	B-Algorithm
batteries	I-Algorithm
usually	O
outlast	O
the	O
system	O
that	O
they	O
support	O
.	O
</s>
<s>
Backup	B-Algorithm
batteries	I-Algorithm
are	O
used	O
in	O
uninterruptible	O
power	O
supplies	O
(	O
UPS	O
)	O
,	O
and	O
provide	O
power	O
to	O
the	O
computers	O
they	O
supply	O
for	O
a	O
variable	O
period	O
after	O
a	O
power	O
failure	O
,	O
usually	O
long	O
enough	O
to	O
at	O
least	O
allow	O
the	O
computer	O
to	O
be	O
shut	O
down	O
gracefully	O
.	O
</s>
<s>
Data	O
center	O
UPS	O
backup	B-Algorithm
batteries	I-Algorithm
may	O
be	O
wet	O
cell	O
lead-acid	O
or	O
nickel	O
cadmium	O
batteries	O
,	O
with	O
lithium	O
ion	O
cells	O
available	O
in	O
some	O
ratings	O
.	O
</s>
<s>
Server-grade	O
disk	B-Device
array	I-Device
controllers	I-Device
often	O
contain	O
onboard	O
disk	B-Device
buffer	I-Device
,	O
and	O
provide	O
an	O
option	O
for	O
a	O
"	O
backup	B-Algorithm
battery	I-Algorithm
unit	O
"	O
(	O
BBU	O
)	O
to	O
maintain	O
the	O
contents	O
of	O
this	O
cache	O
after	O
power	O
loss	O
.	O
</s>
<s>
If	O
this	O
battery	O
is	O
present	O
,	O
disk	O
writes	O
can	O
be	O
considered	O
completed	O
when	O
they	O
reach	O
the	O
cache	O
,	O
thus	O
speeding	O
up	O
I/O	O
throughput	O
by	O
not	O
waiting	O
for	O
the	O
hard	B-Device
drive	I-Device
.	O
</s>
<s>
A	O
local	O
backup	B-Algorithm
battery	I-Algorithm
unit	O
is	O
necessary	O
in	O
some	O
telephony	O
and	O
combined	O
telephony/data	O
applications	O
built	O
with	O
use	O
of	O
digital	O
passive	B-Architecture
optical	I-Architecture
networks	I-Architecture
.	O
</s>
<s>
Cartridge-based	O
video	O
games	O
sometimes	O
contain	O
a	O
battery	O
which	O
is	O
used	O
to	O
preserve	O
the	O
contents	O
of	O
a	O
small	O
RAM	B-Architecture
chip	I-Architecture
on	O
which	O
saved	O
games	O
and/or	O
high	O
scores	O
are	O
recorded	O
.	O
</s>
<s>
A	O
bank	O
of	O
large	O
station	O
backup	B-Algorithm
batteries	I-Algorithm
are	O
used	O
to	O
power	O
uninterruptible	O
power	O
supplies	O
as	O
well	O
as	O
directly	O
power	O
emergency	O
oil	O
pumps	O
for	O
up	O
to	O
8	O
hours	O
while	O
normal	O
power	O
is	O
being	O
restored	O
to	O
the	O
power	O
station	O
.	O
</s>
