General > General Technical Chat
Murphy’s Law with my OBD2 reader
ebastler:
Might it be easiest to just buy a new battery and see whether that takes care of it?
Ideally you can come up with a reason why you always wanted a used battery to play with, e.g. for that small solar panel for your garden shed. Then it doesn’t hurt if it should turn out you bought the new battery prematurely. ;)
tom66:
Not familiar on failure modes for lead acid batteries, but is a high self discharge rate a possible failure? Say some kind of internal breakdown in the insulation between two cells?
AVGresponding:
--- Quote from: tom66 on January 11, 2023, 04:09:36 pm ---Not familiar on failure modes for lead acid batteries, but is a high self discharge rate a possible failure? Say some kind of internal breakdown in the insulation between two cells?
--- End quote ---
The insulation between cells is plastic; essentially the bottom half of the battery is a plastic moulding with another plastic moulded part glued/welded to the top once the electrodes are in. The individual cells sit in wells with the series bus bars penetrating the moulding at the top, above the electrolyte level.
If you had a crack in the plastic wall between the cells I guess it could affect performance in a number of ways, depending on the severity. The thing is, how does this crack happen without obvious external damage? It's an interesting idea, but I think very unlikely.
I'd still be checking the main earth strap resistance, while waggling it, and the main fuse/relay box connections.
edy:
--- Quote from: ebastler on January 11, 2023, 03:58:13 pm ---Might it be easiest to just buy a new battery and see whether that takes care of it?
Ideally you can come up with a reason why you always wanted a used battery to play with, e.g. for that small solar panel for your garden shed. Then it doesn’t hurt if it should turn out you bought the new battery prematurely. ;)
--- End quote ---
Ok so I finally bit the bullet and got another battery (51R type)! :-/O
I've been monitoring my existing battery over the past few days and it's always showing around 12.28-12.32V usually on standby, with battery disconnected at work and overnight, usually about 8-10 hour intervals after driving 20-30 minutes each time (just enough to trickle it back up to 12.4-12.5V before I turn the engine off again). I am able to crank the engine but I am worried about getting stranded. At least having another battery in the "boot" for now is a good idea. :-+
The battery voltage here shows it may be reaching the limits of cranking ability. Apparently newer batteries should be up in the 12.5-12.6V range in "standby". Certainly, my multimeter is not testing it under load. It may drop significantly once the starter is drawing power from it. If it is standing by at 12.3V then it is already compromised significantly. It's just that my car is still able to manage even that low (perhaps in another car or with different driving pattern it would have been considered "dead" long ago).
Secondly, I have *NOT* yet tested the battery leaving it connected in the car overnight and at work. Leaving it connected will keep a few things still drawing power but that take only a few mA. Now I am starting to do that as well to see if it causes further drain, perhaps down to 12.1V or into 11V range for an extended period. Based on my previous tests I am not seeing much current draw when car is off. Nevertheless, if it drops just a bit lower it may be enough to take this mediocre barely-sufficient battery over the edge of the threshold and not allow me to crank the engine! I am not going to keep disconnecting my battery every time I drive the car.
I've looked at various ground points, fuses all look in good shape. Testing connections to chassis, getting good volt measurements. When the battery-testing guys tell me battery still "ok" at ~280-340 CCA (of a 500 CCA-650 CCA rated battery) based on their machine, I don't trust it. I asked a few people and all of them tell me 7-8 years is considered good length of time out of a battery. A few other mechanics told me if the CCA's are getting that low it is on it's final legs.
I haven't returned my old battery for the $20 recycling fee/deposit yet, although I have a few weeks to come back in with the receipt from the newly bought battery and get some money back. In the meantime I just want to try out a few more tests with it outside my car:
1. I'll fully charge it in my external battery charger, test voltage
2. I'll see if I can power a circuit, some 12V device or try using an inverter to power a small bulb.
I'm curious to see how much this battery can still do before I give it back. At this point I don't care if I kill it if I'm bringing it back to recycle..... Unless you think I still can get some use out of it for something, then I'll keep it. But if it doesn't last long on a charge I don't want to throw out an easy $20. Any suggestions?
AVGresponding:
Even once the old battery is as dead as a dead thing you will get some money for it at a scrapyard. Probably not as much as $20 though, unless it weighs upwards of 80 pounds.
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