David Sewell wrote:
My phone switches off a lot and I have to charge it up, but the
battery indicator on the display always shows as fully charged.
Would the battery definitely be at fault? How can I test it ? (it has
four contacts - and is
3.6v ni-nh) I have test equipment.

If it only switches off when you make a phone call, it's probably because of
a dead battery. The battery indicator only shows the voltage of the battery
which can stay high, but as the battery ages, it can no longer give much
current and when you make a phone call, the phone tries to draw more current
than the battery can sustain, the battery voltage sags and the phone shuts
down. If the phone doesn't shut down as easily when you've just charged it,
then it's most definitely due to a bad battery.

If, however, the phone just switches off randomly or when you shake it or
twist the battery, then you probably just have bad contacts. Try cleaning
them all with alcohol or somesuch. On some phones also bending the contacts
outwards can help.

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Arto Rantala