Battery problems

[80Sprint]

I bought a higher capacity battery for my Sprint in the summer and was initially fine. Each time recently I have left the car over a week it loses charge and will not start. I jump started it yesterday and then took it for a decent drive. At least 13.5 volts by the time I got back.
I have been out to the car tonight and the voltage is already down to 11.5. The boot light goes out and so does the interior light.

It seems like it's charging ok so I assume it's losing charge.

How do I know if the battery is duff as I bought it online? I have seen tester put across the terminals before but don't have access to one of those gadgets, just a volt meter.

Anywhere else I could be drawing current apart from the two above ?

[rich]

There is the clock but that wouldn't down the battery that quick I wouldn't have thought,
If you have a halfords nearby they test for free, took two massive lorry batteries there which they did not have a chance of replacing and they still checked them .

[Galileo]

I'm guessing you don't have a multimeter? If you do then you could use the current measurement on that to see what the draw amount is by putting it in series with one of the battery connections, should be in the milliamps for the clock. (Better add, please don't try and start the car or turn electrical items on as most multimeters only do 10 amps at most)

[80Sprint]

I do have a multimeter but only use a couple of the settings. You may guess by now I am clueless with most car electrics. Can you explain please the connecting in series ?
What am I connecting and what result am I looking for ?

Thanks

[Carledo]

There is a very simple test you can do with just a test light or even a bit of wire and a bulb. Or you can use a multimeter set for amps if you have one. Switch off everything you can think of, close all doors and boot. Remove the EARTH terminal of the battery and connect your test light between the earth terminal of the battery and the earth lead. you should get just a bit more than a glow from a 21w bulb. If you get a bright light (or more than about 0.5amps on the meter) you have a big draw somewhere. Now try removing the permanent live fuse (purple/brown wires). At this point, the light should go out. If it does then SOMETHING on that fuse is pulling too much power, clock, stereo, interior light, horn, alarm system (if fitted) that's about all the choices there are. If the light DOESN'T go out with the fuse pulled, the problem lies in something unfused and though there are a few possibles, it will probably be the alternator, pull the plug from the back of the alternator and try again, light out means alternator problem.

Steve

[misterp]

As everyone has said...process of elimination.

Easiest way to start is pull the fuses, key off and then (as Galileo explains) put your multimeter into current setting (you normally have to swap the red lead over to either mA (fused) or a 10A (unfused) port.)

Disconnect the earth lead from the battery and connect in series the meter to the battery -VE terminal (RED multimeter lead to the body and BLACK multimeter lead to the -VE on the battery) and find out how much current the car is pulling @ rest with NO fuses in (this should be virtually nothing)

If you get a reading (let us know here what it is) then there is something wrong/shorting.

From here, if you do get close to 0, then connect a single fuse, and re-measure. This will tell you which circuit the highest current draw is from and then follow the wiring diagram to systematically disconnect each thing in turn to find out the culprit.

Common culrits are car alarms and after-market things that have not been wired in correctly.

Hope it helps.

[AlanH]

Since it seems to drop volts fairly quickly why not charge it up, disconnect it and leave it overnight.

If it still drops, its the battery, if it doesn't get the meter out.

Is it still under warranty?

[trackerjack]

My guess would be a boot light staying on.
I have bought 2 battery isolators that screw down to connect and loosen to isolate I have fitted one to my wifes MX5 and also one to my special that I built, I don't have battery dying now.

[Jon Tilson]

Your first problem is that your battery evebn though its new is now discharged. You must not leave it in this condition or
it will suffer permanent loss of capacity.

So give it a goood long charge on a proper old fashioned industrial strength battery charger - not one of these mickey mouse
electronic efforts.

Your battery will have a specified charge capacity in ampere hours....which means the number of hours it will run delivering a certain load....eg a 20Ah battery will run for 2 hours if its loaded at 10 amps....(quite a high load).

Your alternator would need almost all day running to fully charge your battery, so driving around for 2 hours is nowhere near enough. I guess its rated at 35 amps but wont charge your battery at much more than 5 or 6 I would guess. Once the battery comes up to voltage the charge rate drops right down.

So sort out the battery charge, then just pull off the negative terminal when you leave it standing pending finding out your discharge cause.

As a rule of thumb I reckon a 20 minute drive just about replaces the charge lost from starting...

Jonners

[Howard81]

Not realising the boot light had popped out of place has caused much head scratching for me on a couple of occasions!

[Magenta Auto Sprint]

i away at the moment but back monday, so i can also call round and help with fault finding if you are stilll stuck.

malcolm

[80Sprint]

Battery went on charge all day and the charger showed fully charged.

12.66v was recorded when I disconnected it.
24hrs later it reads 12.22v

Is a small drop normal after coming off the charger. I can check it again tomorrow but where should it stop ideally?

If it drops no more I will connect it to the car and do some more tests.

[lee16v]

hi mike ,my previous sprint had an overnight discharge witch was found out to be a bad altenator,worth a look

[Magenta Auto Sprint]

as mentioned before, happy to call round and help.

I have had an alternator and a radio cause problems when a diode or transistor fails.

Malcolm
(staines massive)

[80Sprint]

Thanks Lee/Malcolm.

The battery is not connected to the car. I need to know first if the battery holds charge on its own, hence my question above. What should a good battery record in volts and should you see any drop after a charge ?