Recommendation -- portable battery jumper

[Brett Dikeman]

Lawrence Bardfeld wrote:

> [Yes, I really did make a good faith attempt to search the archives 
> first.]
>
> Can anyone recommend a portable battery jumper/booster (or whatever 
> they're called) -- or at least tell me what I should look for (e.g., 
> peak amps, or specific manufacturers to avoid)?  Yesterday I 
> unsuccessfully tried to restart my car using a low-powered Coleman 
> unit that was supposedly fully charged, and it didn't work.  (I 
> suppose the connection could have been the problem, but am pretty sure 
> it was secure, so in disgust I'm looking for a better unit.)

It probably didn't start the car because it was sulfated (did you leave 
it for more than 2-3 weeks off the charger in room temperature?) or had 
a shorted cell and cooked itself on the charger (common on very cheap 
batteries or poorly designed chargers, of which there are MANY).  Also, 
if it was nippy and you had a thick oil, that would complicate 
things...one of those jumpers just would NOT have the juice to do it.  
Sulfation shows up as a battery which appears to skyrocket way too 
quickly to its peak charge voltage.  Example- a car battery that jumps 
to 14.4v in a matter of a minute or two at 1A, something that should 
never happen.


There are electrical circuits you can build that will apply VERY short 
but very high current pulses to a battery.  This does work- it causes 
the sulfate crystals to get knocked off the plates and go back into 
solution.  Works very slowly- days to weeks.  They can be built to use a 
tiny amount of the battery's capacity to do so(a few mA) or run off an 
external voltage source, which is more appropriate for batteries that 
are being kept in storage, not seeing regular (at least once a week or 
two) use.

The "jump start" units are just small lead-acid batteries in fancy cases 
with lights and do-dads.  Skip the middleman and buy just the battery- 
digikey.com (a HUGE electronic parts supplier) has these.  You can get a 
decent sized (28AHr or so) Valve Regulated Lead Acid (an evolution of 
the SLA, aka Sealed Lead Acid, or "gel cell") for pretty cheap.  The 
VRLA/SLA's are much better than, say, a "motorcycle" battery, as 
VRLA/SLAs are less prone to self-discharge and sulfation.  Keep it cool- 
the warmer a lead acid battery is, the faster it discharges, and hence 
sulfates.  Also, buy a battery maintainer to go with it- NOT a charger, 
a maintainer.  Battery Tender is pretty well known in this regard; Yuasa 
and others also make units that are very similar (there appears to be 
one or two companies making boards for chargers marketed by several 
companies).

I have a Yuasa unit that's designed a little more for car batteries, 
with a max charge rate of 1.5A instead of the wall-wart units that are 
more like 250mA-500mA for small boats/ATVs/motorcycles.  Like several of 
the other mid-sized units, it has diagnostics and is generally smarter 
than I am (it'll apply a slow current to the battery and watch the rise, 
looking for sulfation, THEN start charging.  It then uses a combo of 
fixed-current and fixed-voltage charging to bring things up to par).  At 
1.5A it can be painfully slow charging a full size car battery that has 
been REALLY discharged; if one comes out that's more like 5A I'll think 
about trading up.  I use mine to top off the car every month or so, keep 
1-2 storage batteries topped up, etc...it generally takes it maybe an 
hour to do so on the car batteries.

Another option- buy an Optima spiral-cell for your car.  The plates are 
VERY large because they're spiral-wound, so a huge # of CCAs.  They have 
excellent deep-discharge tolerance, and very low self-discharge rate (I 
think Optima says you can leave them in storage for up to 6-9mo with no 
ill effect).  No vent tube needed- the battery doesn't vent enough to 
need it.  Shortly after I installed the battery, I left my interior 
light on over 12 hours and the next morning, it started like nothing had 
happened...not sure how much the main light uses, probably 1A or so?  I 
guess a regular battery might take that pretty well too...hmm.

Oh, the solar panel maintainers are also great for countering 
self-discharge and drain from radio/seat/ECU memory.  200mA is pretty 
common; I'd avoid anything rated less than 150mA.  In our cars, you can 
throw it on the back shelf and plug it in via the rear cig lighter (make 
sure child lock is off).

Great site for learning about proper care for lead acid batteries:
http://www.uuhome.de/william.darden/

Brett
-- 
"They that give up essential liberty to obtain temporary
safety deserve neither liberty nor safety." - Ben Franklin
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