Ferrino Posted June 23, 2003 Share Posted June 23, 2003 After having a few starting problems recently, I would like to test the strength of the Varta battery in my 7. Can anyone recommend a good device to test it with? Can I test the strength without removing the leads from the terminals? Also, can you recharge a battery without removing the leads? I was going to remove the leads and give it a recharge with an old recharger this evening, but I was unsure if I was going to whipe the ECU memory or something equally catastrophic. Be gentle on me - newbie alert! Thanks 😬 "An intellectual is a man who takes more words than necessary to tell more than he knows." Dwight D. Eisenhower Link to comment Share on other sites More sharing options...
Chris W Posted June 23, 2003 Share Posted June 23, 2003 Ferrino Firstly you can charge the battery perfectly safely without removing the leads. After all, that's what the alternator does all the time. Even if you do decide to remove the leads to maybe charge it out of the car, you won't wipe the ECU memory. If you have the "plipper" (push button) type immobiliser though, you will need to resynchronise it when you reconnect the battery. To do this, simply push the arming button on the plipper 4 times. On the 4th push you will hear a few loud clicks from under the dash as the unit resynchronises. Then you can push the disarm button to disarm the immobiliser. Always disconnect the negative lead first and reconnect the negative lead last if you remove the battery from the car. If you read my "7 faq" article on batteries you will discover why. Now to your first question - about testing the strength of the battery. Again read the 7faq article for a more detailed explanation. First you have to define what you mean by "strength." There are three possible answers to this: 1. Its ability to provide a starting current. The battery will need to supply close to 300 Amps to turn the engine over. That's a mighty big current. To put it in perspective as to how big this is, 300A at 12 volts = 3.6 Kilowatts!! Since this will vary particularly with temperature (cold days being worse) there is a standard industry measurement called CCA (Cold Cranking Amps) which all manufacturers quote. It's defined as the continuous maximum current the battery can supply at minus 18 deg C (0 deg F) until the battery voltage drops to 7.2 volts. However, a practical test of cranking strength is to turn the engine over with the ignition disabled or the plugs out or whatever to prevent its starting and note the battery voltage. If it falls below 9v whilst cranking, it needs replacing. Note: replacing not just charging! Read 7faq for details of why. 2. Amount of charge stored. The battery is like a reservoir storing electrical energy in chemical form. The maximum amount of energy it can store is known as its "capacity". This is measured in "Ampere Hours" (AH)and (in theory) is the amount of current drawn from the battery multiplied by the time you took it till the battery voltage falls to 10.5 volts. So for example a 30AH battery (like the standard one in a 7) should provide 30A for 1 hour or 15A for 2 hours or 5A for 6 hours etc. However, life isn't that simple and (again to standardise the industry) the official definition is that current which can be drawn for 20 hours without the battery voltage dropping below 10.5 volts. So a 30AH battery really could provide 1.5 A for 20 hours. With significantly higher currents, the theory goes somewhat awry and you would not actually be able to draw, for example, 15A for 2 hours. It might only be an hour. To measure the charge in a battery there are two methods. 1. Check the specific gravity (SG) of each cell with a hydrometer. (see 7faq for details). This method cannot be used with sealed batteries of course. 2. Check the open circuit voltage with an accurate digital (not analogue) voltmeter. 7faq contains a table of battery voltage against percentage charge. Note that cranking current gives no clue as to the amount of charge and, vice versa, charge state gives no clue as to the cranking current the battery can deliver. A simple analogy is a canal lock full of water. The size of the lock determines how much water can flow out (charge), but the size of the sluice gate opening determines how fast the water will flow out (cranking current). 3. The last official measure of strength is "reserve capacity" (RC). This is the number of minutes that the battery can deliver a constant 25A at 80 deg F (27 deg C). This is a useful measure only if your alternator fails because it will tell you how long you may be able to continue driving till everything fails. New batteries nowadays usually have the RC stated on them. This was a long way of answering your question but it was to illustrate that batteries are actually quite complex devices and many factors have to be considered. If you measure the battery voltage off load to get charge percentage (12.6 volts is fully charged) and then measure the battery voltage on cranking load (must be above 9 volts) to get info on its cranking ability you will know whether your battery is of the right "strength". BTW, to make your battery last for years, keep it permanently on a dedicated "trickle charger" when not in use. Don't let it discharge through neglect... it will die on you..... permanently... especially in winter. Chris 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
Ferrino Posted June 24, 2003 Author Share Posted June 24, 2003 Thankyou very much for that Chris - very interesting! I will take a look at your FAQ...... I wanted to make sure that it was safe to recharge the battery overnight while it is still in the engine bay and wired up...... An intellectual is a man who takes more words than necessary to tell more than he knows. Dwight D. Eisenhower Link to comment Share on other sites More sharing options...
Chris W Posted June 24, 2003 Share Posted June 24, 2003 I trust the Eisenhower quote on your post wasn't referring to my long answer. 😬 🤔 Chris 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
Ferrino Posted June 24, 2003 Author Share Posted June 24, 2003 No mate - it's my signature! Bit of an unfortunate choice of quote for when people are trying to help me - looking for a replacement! Have taken a look at my battery and there are 6 removable lids, so I presume I can check each cell with a hydrometer. Will also try to get hold of a digital voltmeter. If I do need to replace the battery, are there any particular brands I should be looking for? Probably a Halfrauds effort. An intellectual is a man who takes more words than necessary to tell more than he knows. Dwight D. Eisenhower Edited by - Ferrino on 24 Jun 2003 09:22:20 Link to comment Share on other sites More sharing options...
Chris W Posted June 24, 2003 Share Posted June 24, 2003 Honi soit qui mal y pense Chris 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
John Howe Posted June 24, 2003 Share Posted June 24, 2003 ... but then he would need to wear garters to keep his socks up! JH Deliveries by Saffron, the yellow 222bhp Sausage delivery machine Link to comment Share on other sites More sharing options...
Ferrino Posted June 24, 2003 Author Share Posted June 24, 2003 OK, I removed the battery and had it tested at Halfrauds - they said it needed replacement. The guy who built the car advises that I get a replacement from Redline, as he used them for all his parts and recommends them. Cheers. An intellectual is a man who takes more words than necessary to tell more than he knows. Dwight D. Eisenhower Edited by - Ferrino on 24 Jun 2003 12:53:54 Link to comment Share on other sites More sharing options...
Tony C Posted June 24, 2003 Share Posted June 24, 2003 Cough BRG SV 😬 aka Bug Killer Link to comment Share on other sites More sharing options...
Ferrino Posted June 24, 2003 Author Share Posted June 24, 2003 I had a peek into the cells of the dead battery and noticed that there did not seem to be a single drop of acid in there. All I could see was the dried lead plates. Weird. Anyway, the Varta battery in there is one used in BMW motorbikes and the best price I could get for a replacement was £62 + VAT!!! The dimensions seem to be very similar to the Banner battery, so I think I might go for one of them instead - I just wish I could find someone local that stocked it. Looks like I may have to go mail order and grab a couple of bottles of acid as well...... Cheers. An intellectual is a man who takes more words than necessary to tell more than he knows. Dwight D. Eisenhower Link to comment Share on other sites More sharing options...
Sheds Moderator Posted June 25, 2003 Share Posted June 25, 2003 If your battery has gone dry this could be as a result of overcharging owing to a faulty alternator. I would check it over when you fit the new batt. Alternatively it could be simply neglect... Link to comment Share on other sites More sharing options...
Ferrino Posted June 25, 2003 Author Share Posted June 25, 2003 Thanks for that - what would I need to check the alternator when I get my new battery - a voltmeter? Any recommendations on an affordable one online? Thanks. An intellectual is a man who takes more words than necessary to tell more than he knows. Dwight D. Eisenhower Link to comment Share on other sites More sharing options...
Chris W Posted June 25, 2003 Share Posted June 25, 2003 Tony To check the alternator (once your new battery is installed) simply check the battery's voltage across its terminals. With the engine off (and the battery charged) you should get somewhere around 12.6v. With the engine running (ie: alternator on) you should get around 14.5v after starting dropping to around 13.5v after a while. If the alternator is giving out 15v or above, it has a problem and will harm the battery eventually. Likewise if the alternator volts are below about 13.2ish then it won't charge the battery properly. I suspect however(due to our offline conversation) that the battery was totally neglected. Chris 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
Ferrino Posted June 25, 2003 Author Share Posted June 25, 2003 Cheers for the info. I have now installed the replacement battery and the engine has started first time (albeit with a few pops and bangs from all that fuel I must have stuffed into the engine when trying to start her the other day?). Anyway, I couldn't find a decent voltmeter, so I kopped out and bought a battery/alternator tester which has 3 lights to indicate the voltage of the battery with the engine off and another 3 lights to show the voltage with the engine idling and the alternator charging. 1) What kind of RPM should I be testing the battery voltage at? It says that 2,000 RPM is the average to test it at, but some engines may need a higher RPM??? 2) Can anyone recommend an affordable voltage meter with which I can get some actual readings rather than a yellow/amber/green light?!? It was cheap, I must admit 😬 3) Are there any visual clues as to an undercharging/overcharging alternator? I guess a slack belt would undercharge my battery? Cheers guys! An intellectual is a man who takes more words than necessary to tell more than he knows. Dwight D. Eisenhower Link to comment Share on other sites More sharing options...
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