| A fully charged battery left for a few hours to settle should read 12.6 volts, any less indicates a battery fault.
for example if one cell is completely dead only 10.5 volts will show on the voltmeter, check again after 24 hours if the voltage has dropped further say from 12.3 volts to 12 volts it strongly suggests a battery fault.
the best way to check a starting fault is to attatch the voltmeter to the battery and attempt to crank the engine you should see a minimum of 9 volts whilst the engine is turning and idealy around 9.5-10.5 volts with ambient temperatures around 20 degrees c.
Batteries generate electricity thorough an iron exchange from the plates to the acid, this process is temperature dependant. as the ambient temperature drops the total current availiable to start the vehicle is reduced and eventually a fully charged battery at around -30 degrees c will only just light a small bulb.
I would suspect the battery first as ambient temperatures have dropped around 10 degrees in thae last month and this will have had a affect on the batteries ability to supply the required amount of current.
also we have seen many gell type and sealed batteries fail recently at work having worked all summer perfectly( I run a car repair workshop)
Also check the connections at the earth cable to frame, the contact at the rear of the starter motor for a voltage drop when cranking as even a small resistence will reduce the current supply at the starter.(to check voltage drop at the earth connect the multmeter one side to the earth(-) terminal on the battery and the other to the engine cases and crank the engine you should see virtually no voltage. to check the starter positive feed carry out the same check from the battery(+) terminal and the starter main contact on the starter motor again there should a negligable voltage shown when cranking if thier is a noticeable voltage shown on the (+) side it could be worn starter solenoid contacts or a bad connection at battery solenoid or the starter itself).
long winded but I hope this helps
dave  |