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Hello. Change battery light on my 22-yr old MX5 has been going on and off for a few weeks. The car also refused to start a few times. Jumpstarting from another car worked well. I am about to get an auto electrician to take the alternator out etc etc - something that will cost me a bit and would like to avoid if I can. The battery itself is an old battery with a slightly bent terminal. A friend suggested changing the battery first as it may have collapsed plates therefore not accepting charges, which make great sense. Advise on what I should do please? Thanks.
I suggest you have the alternator and battery tested before replacing any parts. The alternator can be tested, in place, to determine if it is charging correctly and the battery can be tested to ensure it holds a load (using a multimeter and a battery load tester). A auto electrician should do this for you in the first instance.
Hi there. The AA breakdown mechanic did those testing when he came over about a week ago. He suggested I get the alternator bench-tested by an auto electrician, plus to get the battery changed as well. He thought it was quite 'perplexing' that the alternator was charging on and off even when he was testing it - for example when stationary it was charging fine (most of the time), and when I was driving it was charging half of the time. All in all, not sure what to do exactly. I thought by testing a new battery I would know quite quickly if it was indeed the battery was the problem, rather than spending extra to get the alternator out etc. What do you think? Thanks.
It seems you are in a bit of a predicament. If the alternator is faulty it would be of no use to replace the battery as the fault will still be present and vice versa. It sounds like there is a charging fault and I suggest you have an auto-electrician test the alternator and advise you from there. An auto electrician should be able to test the alternator in place in the first instance by testing from directly behind the alternator charge cable. I am sure a auto-electrician can assess the situation and advise which unit needs replacing/repair in the first instance. A battery that is not fully charged (by the alternator or external charger) cannot be tested correctly.