Battery weirdness

zuutroy

I went to the car there today after not using it for a week and there was no life (central locking not even working). Didn't leave the lights on or anything...Measured the battery and it was reading 2.7V :eek: I thought the minimum possible was 11.8 or something. I'm guessing it'll need a full charge if its reading that low....at a bit of a loss.

gyppo

How old is the battery? I've noticed a lot of todays batteries give up the ghost with little warning. If the battery is 4/5 years old, then its likely to be on its last legs.
Try putting it on charge overnight if you have a charger, but tbh, id be suprised if you get much more out of it.

zuutroy

Its actually only a year old. What happened was I gave it a good clean last week and I think I upset some old dodgy wiring that I did and maybe left something exposed touching metal. I fixed it all up and the battery voltage now seems to be steadily rising from the 2.7V it was reading earlier.

gyppo

Well, fair enough if there has been a load on the battery for a week or so, that would explain it.
Rectify the short/load, and put the battery on an overnight charge, it should be sound then so.

zuutroy

Another quicky. I'm gonna give it a charge...When I'm putting it back, can I throw the multi-meter in between the +ve terminal of the battery and the lead to check if the current draw is still there? What would you expect if all was ok?

Owen

Buy an optimate battery charger/conditioner. They're about 40 Euro, and can recover a deep discharged battery that has sulphated. On top of that, they give you a loom you can add into your car, that provides a waterproof socket you can use to quickly connect the conditioner at any stage, and keep it topped up.

zuutroy

Charging it now with just a regular 4amp charger. It seems quite slow to go up. Been on for 5 hours and currently at 12.1V....which is about 40%......I suppose I'll leave it until bed-time and see how it is. Anyone know what it would need to be at before it has a chance of starting the car?

hiluxman

i think its supposed 2 be 12.8 volts with the battery disconnected, a 4 amp charger, that will take forever

zuutroy

hiluxman wrote:

i think its supposed 2 be 12.8 volts with the battery disconnected, a 4 amp charger, that will take forever

Ha...I'm finding that out...for some reason it's only drawing 1.5 Amps too...I'll leave it overnight and see what happens.

okcomputer

did this work?

Gurgle

zuutroy wrote:

Another quicky. I'm gonna give it a charge...When I'm putting it back, can I throw the multi-meter in between the +ve terminal of the battery and the lead to check if the current draw is still there? What would you expect if all was ok?

If all is fine, current draw should be well under 1A.

A fully charged battery can supply a couple of hundred amps at 12V. Your average multimeter can measure a max of 10A.
I would expect the fuse in the multimeter to blow if theres a short. Then your meter will show 0A.

With the battery out, measure the resistance between the positive and negative leads.

It should be in the region of KOhms to MOhms, depending on whether you have an alarm & central locking and whether your radio draws a bit of power to keep your presets.

zuutroy

okcomputer wrote:

did this work?

Yep its fine now after a very slow charge (1.5 days)

daedalus2097

I've come across a couple of cases where a relay can stick in the on position after the car's been turned off, and this can lead to running down the battery like that. Could also be something like the fan thermostat sticking so the fan was running for a couple of days - but you'd probably have noticed that.

The 4A charger is only giving 1.5A as the battery is nearing its full voltage. Constant voltage chargers work this way - as the battery approaches 12.8V or so, it's almost the same voltage as the charger's output and therefore there's very little potential difference for current to flow across. A simple and cheap solution for not overcharging the batteries.