chris956 Posted January 8, 2015 Share Posted January 8, 2015 Long story short , mums car is off the road and her battery is flat. Dead as a dodo. Its a relatively new battery and has been on the optimate / conditioner before to keep it topped up. Forgot about it for a few weeks and the alarm has drained it to nothing.I`ve had it off the car and plugged into my conditioner / optimate for a couple of days now and the gadget tells me all is well. I have put a meter across the terminals and it started at 13.18v. A day or 2 later and the same battery is now reading 13.03vIs the only way to "really" check if the battery is ok , is too do a load check with the car running ? Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted January 8, 2015 Member Share Posted January 8, 2015 There are cleverer tests that need more equipment. but for the vast majority of 7 situations you need to do the following first: Check fluid level. Measure voltage across battery at rest with ignition on. Ditto while cranking or attempting to. (The poor man's load test.) Ditto at 3,000 rpm.This needs a multimeter costing about £12. As far as I can tell many of us can't do it reliably with an indicator on a charger, from the brightness of the lights or by estimating the speed of cranking.There are many examples in the archives of members wasting time by not doing this early in the diagnostic process.Jonathan Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted January 8, 2015 Member Share Posted January 8, 2015 I have put a meter across the terminals and it started at 13.18v. A day or 2 later and the same battery is now reading 13.03vIn which of the three conditions were those measurements taken?Jonathan Link to comment Share on other sites More sharing options...
Paul Deslandes Posted January 8, 2015 Share Posted January 8, 2015 The old way was to put a 'tong tester' across the battery which imposed a huge load for a few seconds whilst checking the voltage. I haven't seen one of these for a while but your local auto electrician will probably have one. Alternatively, check the voltage whilst cranking which is what the tong tester is simulating.If it's been charged for a long period, i.e more than three days, it should reach 13.8V. What's the voltage when the car engine is running and charging the battery? It will depend on the alternator but should be 14 - 14.2V 'ishCan you borrow a proper charger to give it a few amps for a few hours? Most conditioners don't deliver enough current to bring a severely discharged battery from the dead. Provided it's not too old and hasn't been flat for too long you stand a good chance of reviving it.Paul Link to comment Share on other sites More sharing options...
chris956 Posted January 8, 2015 Author Share Posted January 8, 2015 To add, the voltage was taken after checking and filling the compartments with water and then just having the battery sat on the floor disconnected. I was wondering if the charge level should settle at all ? I will re attach to car and check the cranking voltage. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted January 8, 2015 Member Share Posted January 8, 2015 If you only measure at rest (after adequate charging) you can know that the battery is U/S if the voltage is too low, but you can't tell for sure that it's good.Jonathan Link to comment Share on other sites More sharing options...
chris956 Posted January 8, 2015 Author Share Posted January 8, 2015 What would the voltage have to drop too , to point towards it being dead ? Link to comment Share on other sites More sharing options...
Paul Deslandes Posted January 8, 2015 Share Posted January 8, 2015 Once charged and allowed to settle after being off charge for an hour or two it should read about 12.5V. When fully charged and cranking it can drop to about 9.5V but 10.5V is better. The voltage will vary with temperature. Try Googling battery charging and you'll find lots of info, some good, some rubbish! Also check the Blatchat archive as this topic has been covered a lot in the past.TBH, unless you want to splash out on a new one, understandable if you don't want your Mum to be stuck somewhere with a dead battery, I'd fully charge it over two or three days, put it in the car and then try to start it the following day. If it sounds healthy and starts the car, it's probably okay. As you've topped up the electrolyte, If you can borrow a hydrometer you could measure the specific gravity but this isn't a particularly reliable measure. I have an Isuzu Trooper with two, big, five year old batteries, both of which had in-spec SGs, but they wouldn't start the car for toffee! Link to comment Share on other sites More sharing options...
chris956 Posted January 8, 2015 Author Share Posted January 8, 2015 Okay guys, thanks for the info.... Perfect. Will check the stabilized voltage then refit and double check. Link to comment Share on other sites More sharing options...
chris956 Posted January 12, 2015 Author Share Posted January 12, 2015 Bolted back into car and was seeing 9.5v on cranking and 14.3v at 3k revs ..... Is that good ? Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted January 12, 2015 Member Share Posted January 12, 2015 9.5 V while cranking is lower than comfortable. The battery may be starting to fail, and it seems that some ECUs won't work reliably if you get below that, so that even though it cranks it won't start.Charging is OK. Jonathan Link to comment Share on other sites More sharing options...
Paul Deslandes Posted January 13, 2015 Share Posted January 13, 2015 9.5 is at the bottom end of just about okay ('ish). A very cold engine (thick oil) will accentuate the issue.You pays your money and takes your choice. New battery and issue gone away. Sleep easy. Keep the old one, keep it charged on a conditioner, probably be okay for a while but always nagging worry that you'll get a call from Mum stuck with a flat battery somewhere. Link to comment Share on other sites More sharing options...
chris956 Posted January 13, 2015 Author Share Posted January 13, 2015 Yes it was cold etc etc. The car has been sorn'd now as not used so no issues about being stranded. Plugged into conditioner to keep alarm active. Could be a low mileage hardly used Megan's cabriolet for sale soon as mums health means no more driving :-( Link to comment Share on other sites More sharing options...
Graham Perry Posted January 14, 2015 Share Posted January 14, 2015 Another simple test. Remove the covers for all the cells on the battery. Swich everything electrical on on the car. Then get someone wearing safety glasses to look at the cells while somone else cranks the car. If one cell is bubbling significantly more than any of the others under load then the battery is toast. Link to comment Share on other sites More sharing options...
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