Hi,

I've bought a max/min multimeter as recommended by you all.

The voltage before I started the car was 12.2V

When I started the car the voltage dropped to 9.1V minimum during
staring.

Once the engine was running, the voltage was 14.5V maximum.

Am I right to be worried about the 9 volts? It seems low to me but
OTOH I am not having any problems starting the car at the moment, so
isn't that the biggest test of the battery?

I compared it to my other half's car and the voltages for that we
12.4V before, 10.1V during, and 14.6V after starting.

By the way, the multimeter claims to have two settings to test 1.5V
and 9V batteries. The manual claims it puts a small load across the
battery and displays the voltage. Anything about 1.2V is ok for a 1.5V
battery, and anything over 7.2V is ok for a 9v battery, or so it says.
I had some flat 1.5V batteries that measured 1.25v, so they passed the
meter test but were useless in practical terms. Are these [non-car]
battery test settings a waste of time? I seem to remember that when I
was at school we were told you should test a battery by its current,
not its voltage?

TIA