Flat Battery or Bad Alternator or ???
 

I've got an old and somewhat poor condition 1999 MX5 that has recently developed a problem. I'm hoping someone can advise me, I'm somewhat useless with cars - so any even basic help is much appreciated.

This is what has happened:

December 1st - After being parked for a couple of days, the car battery was completely flat, no lights or electrical response at all.

December 10th - A friend helped me jump start the car. After jumpstarting, I let the engine run for 10 minutes, then (because it was dark) switched on the lights to take the car for a drive. The instant I switched on the lights the engine died. I jump started the car again and this time drove around slowly with the lights off for 15 minutes (10-20mph). Then I tried the lights again and the engine died again. I noticed that there was a bit of an electrical flickering noise when the headlights were turned on. Reverse, indicators etc were working fine while I was driving.

December 20th - I intended to take the car to a garage, so I got my friend to help me jump start it again. This time, whenever I tried to pull away, the engine died. When the car was sitting stationary, there was a noticable flicker to the light that illuminate the interior clock. The car has since not been moved.

What do you think the problem could be?

I'm not sure about the initial cause of the flat battery - I could have left an interior light on. I'm not sure.

It seems strange that after being completely flat, I was able to get enough charge into the battery to drive for 15 minutes in the dark, but then 10 days later, I wasn't able to do the same thing again. By the way, the gaps in the time-line above are because I've not got a friend in my city that I can immediately call on for jump start help.

I use the car as a basic run-about. It is a car that was given to me in poor slightly rusty condition, but I'm thankful for it as it gets me from A->B. I'd really like to revive it if I can, but can't justify spending a lot of money on it.

Is there any way to tell whether the battery or the alternator is the problem? Do the symptoms I describe suggest one or the other?

If I could find a used alternator in ebay or something I could get a mechanic to fit it for me. Likewise I'd be happy to replace the battery.

Any help very much appreciated.

Thanks!

Basically you need to jump start it again, however leave the jumper leads connected for about 15 minutes. After that, take the jumper cables off, you then need a multimeter to check the charge rate of the alternator. Then you need to fully recharge the battery & then get it load-tested.

This will tell you if the battery or alternator is at fault.

sounds to me like a bad alternator. if the alternator is bad, it wont charge the battery. whant to make sure? do like the grim reaper says. measure the battery voltage. then start the car and measure again while the car is running. the voltage should be higher than the first reading. or, remove the alternator and battery and go to advance auto parts, they can check both probably for free.

Thanks, I'll try this. I've got a multimeter so will give it a go later today.

Just to be clear, am I right in thinking I should jump start the car - then leave the battery connected for 10 minutes?

you can measure, jump start the car, remove the cables and measure at that moment. no need to wait. the situation you describe makes me suspect the problem is the alternator, because the car dies when the battery is drained. for the battery, just remove and get it checked and if good, get it recharged.

Sadly I saw your message only after I had my friend helping me jumpstart.

A passing breakdown repair guy also stopped and helped me/ He measured various things with his multimeter and said that it would appear the alternator is fine as the voltage when running was higher than when switched off. He reckons the battery is damanged, maybe with a dead cell.

Sadly there was nowhere to buy another battery. My local place (within walking distance) doesn't seem to stock 053 batteries, which would appear is what the MX5 needs. I see some sites saying that a 063 battery fits the MX5, is that right? Can I use one of those (or any other models) instead?

Thanks

that, my friend, is up to you. what battery to buy.... if you live in a place with cold weather, get the biggest monster you can fit in its place (in terms of CCA). but im still suspecting about that alternator. again, i have been wrong before, i might be wrong now. do you remember what voltage did the guy with the multimeter got?