Car battery jumper packs

Then I think we will have to agree to differ. ;-)

Pushing anything past it's ideal limits to simply test the functionality of something else (in a non critical or specifically 'testing' environment) isn't 'ok' in most cases in my mind. YMMV of course.

Interesting though. ;-)

Cheers, T i m

[...]

The alternator output is fairly irrelevant as its full output would be much too high for the safety of the battery.

The generally accepted maximum safe charging current is the capacity divided by five. A typical 60A/hr car battery would then have a maximum charging current of 12A.

Even if systems such as Ford Smart Charge, which 'guestimate. battery temperature in order to allow higher charging rates from cold, increased that to 20A, 20 minutes driving would be a long off of recovering a

*completely* flat battery to a state where it might start the car.

Chris

[...]

How many times have you jump-started a vehicle and the battery continued to give good service afterwards?

Chris

We would also have to disagree that flattening a battery once or twice during its lifetime, provided it is recharged promptly, won't kill it. I'm pretty sure all the evidence is in my favour!

You still didn't attempt to answer my good question; what would you do to ensure that jumper pack would start your car if the battery was flat?

Chris

A jump start is usually the beginning of the end I agree, but usually a short drive will recover a battery to some extent.

I have found you can get to a point where batteries can become 'summer batteries', that is they are fine when it's warm and you haven't been using a lot of load when running, like lights and rear-screen-heaters etc. As soon as it becomes cold and with long nights, that's when most batteries are under the greatest load and when their *capacity* is put to the test.

In my small heap of batteries to go to the scrap are many that will charge up easily and hold their charge well but have simply nearly no capacity.

This is also something my mate found out when both power feeds to the datacentre he works at failed and the UPS's couldn't hold on long enough for the generators to kick in. ;-(

Cheers, T i m

I have never suggested for one second that it would.

For the above, yes (never contested), however there will be some loss of efficiency otherwise it wouldn't be the general recommendation to

*not* allow the battery to discharge past 50% / 10.8V and if allowed to get low / flat to charge it up (fully) asap. All you are doing by following that advice is to minimise the damage, it would never be recommended.

I believe I gave a perfectly good answer, and that is (given your restrictions on test gear / old batteries etc) then the answer is there *isn't* a way.

In just the same way there isn't a safe way to test a suicide pill or the dedication of a Kamikaze pilot. ;-)

Cheers, T i m

It depends on just how flat. If a battery is totally flat - like because of the lights being left on to extinction and beyond, the car generator may never charge the battery at all - even if jump started. All you can do it put the battery on a external high voltage charge and hope it might recover. And it could take days. Pulse charging is another way.

The battery being just low enough not to start the car is a different matter.

My experience is that soon after I have completely flattened a battery it will have reduced capacity and fail soon after.

YMMV

Minis never did. Minor 1000s are the last I can recall, but I thing Mr C's 2CV beats that.

Your preconditions for that question are very much "I wouldn't be starting from there".

I'd see what it did with one of my old knackered batteries in the car.

But the way that a knackered battery will respond is different to the way a part discharged good battery would be. So the test might be inconclusive in a negative way toward the battery pack.

Quite. ;-)

Like this: ;-)

Yes, where 'knackered' = very low in capacity and possibly some charge but otherwise good (for reasons MrC mentions later).

The point being, whilst Chris's scenario (running your battery down till it's below engine cranking point to test a jump starter pack) is a perfectly valid real world test, it may not be without cost and ironically, to the very thing that may be paying the price in the first place, the battery. ;-(

Cheers, T i m

I have been considering adding a battery test in when I carry out a service, at present I just do a simple load test to see that it stays above 10v, but I see that the new capacitive type testers include state of health and a check of actual CCA capacity, which might be better to know. Problem is that there are many different testers available and value/quality are both issues, they can also come with a printer or pc connector, and do I want one that shows internal resistance? Any thoughts??

Ok.

So that gives you CCA and a general idea that the battery isn't failing internally etc.

Yeah, I think the AA guy who responded when the aux battery failed in the SL63 recently had some such gadget.

I'm afraid I'm not really up on commercial gear and only have the old manual high current tester for CCA and the ACT capacity tester:

Plus std DMM and the iCharger that I think can display internal resistance etc, 1010B+ (more for Lipo etc)

and PC based logging software for printing charts.

I think I can see where you are coming from though and people can often better understand what they can see on paper (and of course if done (technically) correctly, can't be 'questioned' for it's validity by anyone else).

A mare who has run his own garage for 40+ years now takes digital pictures of all the work he does for new customers or anything that is a bit unusual as he goes along and gives anyone who is interested a little slide show of what he has done. Many seem 1) appreciative of his level of effort and 2) because they then have a better understanding of all the work that has gone into doing whatever they are handing their 'hard earned' over for, do so feeling they have got good vfm, they then better understand what they are actually paying for.

I'd say nearly every car that he takes on that was supposed to have been dealer serviced has never had the rear brake drums off.

So, with the right gear you could give them a battery health check printout (worth more to them than you just telling them (IMHO)) and 'value adds' what you are offering them in the same way it might if you gave them the printout from the aircon machine or the brake test or exhaust gas etc.

If it were me and I wanted to be proactive on the battery pov, I think a decent instant capacity tester with printout (that truly reflected the battery capacity) could be use to both give you a bit more (genuine) work plus possibly save your customer from getting caught out (and the potential of you getting the 'blame' because you were supposed to have serviced their car)?

So, if a supposedly 60Ah battery only tests out at ~20Ah and it could be the original or was obviously not that new and the winter was coming, it might be good to mention such to them.

Cheers, T i m

In the past I have actually sat and measured the mA/hour of a lead acid battery on charge and discharge. I.e a totally flat battery charged then discharged at the claimed capacity. Such things keeps me amused.

I should have clarified at 1A/hour rating

Been touched by the hand of a factory trained technician, that's as good as being touched by a magician. Everything gets restored back to factory fresh.

Bet most of them over 4-5 years old don't have working thermostats.

Never had a coolant change.

Never had a full brake fluid change that purged the rear cylinders.

Air filter? It will be a greasy black thing with as many years of crap on it as the car is old.

Spark plugs. OK iridium from the factory last 5-6 years. So why has it now got copper that only last 1/2 a year?

Can you date a factory oil filter?

But £40 for a pair of wiper blades, thank you sir!

Yep, basically my thoughts plus a couple extra. Some main dealers I know of send video of what they find when contacting customers to OK extra work.