Flat battery - is it my radio?

Post by **kas279n** » Wed Jan 30, 2008 1:41 pm

Hi there,

I've now picked up my Moggie Traveller - she had a good run on Saturday and Sunday as I drove her everywhere! and then to work on Monday. She got left in the garage yesterday and then wouldn't start today as she now has a flat battery - there was nothing in her at all. She's got a recon engine with an alternator, so I would have thought the drive would have given the battery a good charge.

I asked the chap who I bought the car off (he's someone that restores and does moggie mechanics) to fit a radio that I provided them with, which he did. I deliberately bought a face off one so there was as little charge draining the battery as possible when the car is not in use.

I'd really appreciate your thoughts before I go back to him to say she's not very well...

In the meantime, I'm pleased to say I have a plug in battery charger so should be able to get her going soon.

Thanks in advance for your thoughts and opinions...

Kathryn

Post by **Orkney** » Wed Jan 30, 2008 1:50 pm

Chances are the radio might use a miniscule amount to retain its memory (shouldnt matter if aface off one or not as far as that goes), but not enough to flatten your battery.

Could just be the battery on the way out - its the time of year for it. That or its not charging corretly so potentially an alternator / dynamo problem.

Post by **bmcecosse** » Wed Jan 30, 2008 1:53 pm

Or - maybe the side lights were left on - or a door slightly open if the interior light works ? More serious problems would be faulty alternator - can reverse drain when not running, yet still charges when IS running. Or poor battery connections/bad earth cable - or knackered battery although that doesn't usually happen 'suddenly'!

Post by **kas279n** » Wed Jan 30, 2008 1:56 pm

I know the lights weren't on - I checked that as soon as I realised the battery was dodgy. The interior light only works when I switch it on (it doesn't function with the doors open/shut) but I did use it on Monday, so that is a possibility... I'll charge the battery tonight and see what happens! It was a sudden fault as she's been starting beautifully.

Post by **bmcecosse** » Wed Jan 30, 2008 2:01 pm

Oh well - as you say - charge it for a couple of hours or so then see if it starts.

Post by **Rob_Jennings** » Wed Jan 30, 2008 2:02 pm

A 'face off' radio do not consume any less than other radios on standby. Modern radio should only pull a few mA when off, just enough to hold settings.

The only way to check what the radio is consuming is to turn everything off (including the radio) and introduce an ammeter in the circuit.

it could easily be something else in the car that's causing a draw on the battery (faulty alternator, bad door light switches)

Now given you you were happily running about for a few days and simply left it over night, even if the radio was left fully on that's not likely to have completely emptied the battery. Did the lights and things work before you tried the starter? Common failure for a battery is for one cell to fail, but this normally happens at a point of high demand (starting) but before that point lights and other things all appear to work fine.

It really suggest you were not actually charging the battery properly (alternator fault, loose fan belt ?) or that the battery simply has given up. Batteries can and do stop working just like that, caused by rubbish floating around in them. I've had batteries that stop after 3-4 years others that seemed to last forever. Worst thing you can ever do to a lead acid battery is fully discharge it, that's a sure way to reduce its capacity and life or kill it completely.

Check the battery is topped up and in good condition, also if it is date stamped how old is it? (5Years = old). Once you get a jump start check you are charging the battery. A fast idle / medium revs should give close to 14v across the battery, less then this will not charge it. Turn on full lights etc you should still read 13+ volts at a medium revs, otherwise your alternator is not keeping up with the load (poor alternator or slipping belt). With every thing off disconnect the battery and put an ammeter in circuit to check for unexpected drain (expect 10-50mA for standby of radio, clock or anything else in the car, nothing more than that). if all that check out then afraid its new battery time.

Post by **Orkney** » Wed Jan 30, 2008 2:02 pm

Dont forget the fan too ! I'd always be forgetting that if i wasnt blessed with the screech from hell

Post by **bmcecosse** » Wed Jan 30, 2008 2:14 pm

Fan ? Heater fan would normally be through the IGN circuit, and you should do the same with a radiator cooling fan if that's what you have ? i know some cars put it through the non IGN circuit with a thermostat (or timer) to sitch it off after the engine stops. I can never trust them - and when I had car like that I always had to stand and wait for it to go off before walking away!

Post by **Orkney** » Wed Jan 30, 2008 2:20 pm

Sorry BMC - did mean the heater fan.
Scab's is definitely not through the ign circuit.
Great advice there Rob !

Post by **crossword** » Wed Jan 30, 2008 2:39 pm

Try charging the battery , disconnect the earth lead , leave overnight or for 24 hours or more , reconnect & try to start . If its dead it must be the battery self discharging . The reason for choosing the earth lead is safety, Ifyour spanner touches the positive & the body at the same time you willget sparks & possibly a spanner welded to the body . No such risk with the earth .

Post by **jothina** » Wed Jan 30, 2008 6:51 pm

is your radio connected through the ignition, ( does it switch off when your turn off the ignition?) i had mine connected to a unswitched live so i could use the radio without the keys in the ign and was fine untill the car was left unused for 3 - 4 days and it drained the battery flat, not even a twinkle from the int light, this was a new batt and alternater

Post by **Rob_Jennings** » Thu Jan 31, 2008 12:32 am

most radios have a permanent feed (thin power wire) and a switched feed (thicker power wire) you really should use those as described. But most modern units in standby use almost nothing, you can confirm that with an ammeter is series with the unit turned off.

Post by **Mogwai** » Fri Feb 01, 2008 8:39 pm

Heres a chart that may be of interest It shows the max permitted absorption of batterys with ignition off. Its geared towards modern cars with higher levels of electrical accessories but is still useful

battery capacity max permited absorption
32 Ah - 19 mA
40 Ah - 24 mA
50 Ah - 30 mA
60 Ah - 36 mA

max absorbtion = 0.6 mA x Ah (battery capacity)

Post by **Kevin** » Sat Feb 02, 2008 8:06 am

It shows the max permitted absorption of batterys with ignition off.

Excuse my ignorance but what exactly does that mean in english.

Post by **Mogwai** » Sat Feb 02, 2008 11:57 am

sorry not very clear when you look at it I just copied what it said on the chart I have. Alarms radios & any other electronic gadgets that operate when the car is not used consume a very small amount of power even when off. if the battery is too small it will go flat quicker more of a concern on modern cars with lots of pointless & unnecessary electronics on them than a minor but a faulty radio or alarm could draw too much current . to test disconect a battery lead put an ameter in the circuit between he battery & the cable with everthing turned off the reading should be next to nothing.