[Healeys] Portable battery jump starter

[Bob Spidell]

Here's what I'm not getting: When you go to buy a car battery, what are 
the numbers you check first?  OK, price, but then you look at: 
warranty--usually given in months (72, 84, etc.), and cold cranking amps 
(CCA).  We all know the warranty doesn't guarantee how long the battery 
will last, but how much of a pro-rated 'refund'--usually a credit 
towards purchase of another battery of the same brand--you'll get if the 
battery expires before the warranty period ends.  CCA gives a 
rough/reasonable approximation of how much current--i.e. 'power'--the 
battery has to supply in the burst necessary to wake a starter and turn 
an engine over in freezing weather (more should be available in warmer 
temps).  Depending on application, you're gonna want at least 500 CCA 
for any car battery, esp. an older car without a geared reduction 
starter, and more is better (a typical, non-geared starter in good nick 
pulls, I think, about 200-300 amps for a split second--until the 
inductive load builds--and you want a margin).  The AGM battery I bought 
recently for my BJ8 has, IIRC, 800 CCA.


These 'pocket' jump-starters typically give their 'power' in 
milliamp-hours, or mAh.  This is a number usually given for a power 
source that is expected to maintain a minimal current over a period of 
time; i.e. hours.  Further--I'm not an EE or battery expert, don't play 
on TV and haven't stayed in a Holiday Inn for years, so FWIW--to my 
knowledge Li-Ion batteries are known for just that; supplying a steady 
current over time (like in your cellphone or Tesla).   I'd be interested 
in how many CCA these jump-starters promise; I don't really care if 
it'll power my iPhone for 100hours.


The problem, I'm surmising--if you're a battery expert please chime 
in--is that if you're attempting to jump-start a car with a totally dead 
battery the dead battery will sink a bunch of the current from the 
starter battery, hence that current won't be available to rotate the 
starter armature.  Which reinforces my experience that, if you're 
attempting to jump-start a marginal battery these might get you over the 
top, but if you've got a completely discharged battery--and it's 
cold--well, good luck (which begs the question: Should you disconnect 
your dead battery and attempt to jump directly to the disconnected cables?).


Also, if you've bought jumper cables you've found that the good 
ones--with, for instance 'double-ought' (00) gauge wires--cost 
significantly more than the cheapies, which might be #2 gauge. With 
cheap jumper cables, you're going to put as much energy into heating the 
cables--and probably get a drop of a volt or two--as you are into the 
starter.  The pocket jump-starters I've seen all have really wimpy 
cables, which can cause a significant voltage drop.


Bob


On 4/29/2018 6:43 AM, White, Stephen wrote:
>
> I got the "Viking compact power pack" from harbor freight - 
> worthless.  Never did have punch for car battery, won't even do a 
> motorcycle now. (a year later - used only for attempted 4 jumps)  
> listed as 12V 12000mAh.
>
>
>
> ------------------------------------------------------------------------
> *From:* Healeys <healeys-bounces at autox.team.net> on behalf of John 
> Spaur <jmsdarch at sbcglobal.net>
> *Sent:* Saturday, April 28, 2018 1:25 PM
> *To:* healeys at autox.team.net
> *Subject:* [Healeys] Portable battery jump starter
>
> I would like to get a portable battery powered jump starter. They 
> range in price from cheap to expensive. Any recommendations?
>
> TIA,
>
> John Spaur
>
> San Jose, CA
>
>

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