Car battery jumper packs

Best one was my BMW 528i SE auto. I bought it at two years old with a full service history. Handbrake was poor, and I mentioned that at service time. But being an auto, I never really used it. Full main dealer service history. They also did the first MOT. The second MOT I had done elsewhere. It failed on the handbrake. Had some time spare that week, so I investigated the handbrake myself. One adjuster was locked solid on minimum. Had to remove it and put it in the vice to free it. Once free, it moved easily. The cable on that side had been pulled up tight in an attempt to get that brake working at all. Resetting it all got the handbrake working to spec for the very first time in the car's life. That was just one of the many many reasons why I'd not trust a BMW main dealer. Only to keep the service book up to date while the car was worth something. After that I used a local specialist who were not only cheaper but honest.

The dealer I used changed hands a couple of times while I was using them. With no improvement. They've closed down now.

Thanks, that reduces the choices a bit.

I have done the exact same thing (clock, multimeter and notepad) but now I have some kit that will do it all for me. ;-)

The most pertinent time was when designing, building and racing 'Electralights' and we were only allowed 25kg of battery. So I searched for a 12V battery that was as near to 12.5kg as I could find (as I ran a 24V motor) and borrowed all of that model the local car spares place had in stock for the weekend. I measured the reserve capacity (the time in minutes a battery can deliver 25 amps at 25DegC until the voltage drops to 10.5 volts for a 12 V battery), selected the best matched *pair* (neither of them offered the best reserve capacity etc) and took the rest back. ;-)

The batteries really got a caning but in that role they were considered 'consumables'. ;-)

Cheers, T i m

Only comment I'd make is testers like the ACT (which is what I have) require an excellent connection to the battery to be accurate. Which usually means disconnecting it. I noticed a test being done on a car at Halfords with a similar device and they just connected it to the terminals. When I've tried that here, you get a lower amp.hr reading than direct from the battery posts.

I think any true / technical work being done on / to a battery can only really be done with it disconnected (and also at the right temperature).

Cheers, T i m

I see that some units have a setting for 'on car' or 'off car' Perhaps that offsets the readings to compensate? I can see how a less than perfect connection can alter the readings.

The ACT compensates for temperture. It's a very clever device.

I simply don't know.

If used on car a chargers clips/grips will be fastened to the battery connectors. If used off car the connectors will be directly to the terminals and 4 possibilities i.e bad connectors at the on car battery will be removed from the equation. Basically an off car test is far more reliable.

True. I don't know how you could get a reliable reading of what is based on the internal resistance of the battery if going through the terminals - unless you knew exactly how much resistance they added.

Yes, it (mine) compensates for the *ambient* temperature (of the unit) but wouldn't compensate for a cold battery I'd just taken off the car and brought indoors.

It's a fairly clever device. ;-)

Now, my 'Intelligent charger / discharger / cycler has an external temperature probe ...

Cheers, T i m

Then take the meter outdoors. ;-)

A proper one would probe the actual electrolyte temperture. As once was the case. But you only really need that for fast charging.

Quite ... but you would still be advised to allow the meter (or battery) to acclimatise before taking any serious measurements. ;-)

As you say, 'as was once the case' as many (most?) batteries, even lead acid SLI (and especially most portable cell chemistry these days), but now mostly impossible.

Yeah, that is what it's 'mostly' used for on my intelligent charger ... charge management / overtemp protection, along with capacity measurement (there are internal and external temperature sensors).

Cheers, T i m

Once is not going to do the battery any harm at all.

Flattening it to near zero (as in won't turn the sidelights on) then leaving it a week will damage it (sulphating) but this will not.

Not aware of the Mini having one - mate had a 1963 Morris Mini and no evidence of a starting handle that I recall.

I do remember the Minor 1000 - we even used it occasionally for real.

I agree. My Touran was needing a jump start after sitting for a week. New battery and it has not let me down.

The only exception I can think of would be a once off extraordinary drain on the power - say a caravan hooked up or leaving the parking lights on too long.

Caravan electrics aren't normally powered from the car. Even if left hooked up power is supplied via relays that only work with the engine running.

Tim

I know - I was thinking of the fridge in transit mode, but I suppose on a 13pin plug or 2x7pin that would only energise when the ignition was on...

I had a 1963 Cooper - no handle there. In fact I couldn't imagine how it'd connect to the crank pulley - but it obviously could, looking at the aftermarket kits.