No
On 20/11/2017 01:09, Johnny B Good wrote:
On Sun, 19 Nov 2017 21:22:41 +0000, newshound wrote:

On 19/11/2017 11:16, Dave Plowman (News) wrote:
In article ,
newshound wrote:
IIRC this was originally an 80 amp-hour battery and it certainly still
provides more than 10 AH at 12 volts, based on the lights that I run
off it. And it is usually powering a couple of PIR lights that also
get triggered through the night by cats, foxes, etc, so I suspect it's
doing better than that.

My posh tester tells me a lead acid needs to be replaced when the
nominal capacity drops by more than 20%. ;-)

And that might well be a reasonably criterion for an automotive battery,
especially measuring at normal temperatures since the performance drops
with temperature.

But this one is still doing its job, although it looks as though one
cell might now be shorted, since this one isn't gassing. Didn't have a
DVM to hand but will check the voltage tomorrow.

The battery is obviously of an age where you'd expect the side effect of
loss of plate material to accumulate in the clearance space at the bottom
of each cell to become a source of high self discharge leakage, if not to
the point of shorting the cell when you've lost more than 75% of capacity.

Initially the worst effected cell loses charge from self leakage which
exacerbates sulphation, further reducing capacity such that you get a
runaway effect, perhaps mitigated by applying a gassing charge that
ensures *all* the cells start gassing on each charging session,
necessitating a top up of water where the best cell needs the most with
the worst needing the least amount of topping up. However, once you've
reached this stage, the situation rapidly deteriorates to the point where
no amount of gassing charge and gallons of distilled water can mitigate
the final demise of the battery.

A sure fire sign of a 'shorted out cell' is the resting voltage, hours
to days after receiving a full charge, settling to a mere 10.6 volts
instead of the more typical 12.7 volts. I'm guessing those 12vdc CFLs use
an electronic ballast that can compensate for the reduced voltage, so,
unlike an incandescent filament lamp, can hide this symptom of low
battery voltage by the other, not quite so obvious one of shortened
autonomy which might well be hidden by a regular recharging schedule that
prevents the remaining "good" cells from becoming totally discharged.

I can see some benefit in making use of a worn out high capacity car
battery for light duty where the fractional capacity is enough for a
month or so's worth of autonomy when it's not kept in a secure location
wherein the sheer weight (of a boat anchor) becomes a nice deterrent
against theft but, IIRC, I believe you keep it locked away in a secure
shed where you might be better off using a much lighter 25AH SLA instead.

Thanks for thoughtful comments. Didn't get to check the voltage yet (mad
day today) but I will do ASAP. I agree, I think these "caravan/boat"
CFLs cope very well with low voltage (which is probably part of the
design spec). One of the huge advantages from moving to "12V" lights run
directly from battery instead of what I used to do, using a cheap
inverter with mains CFLs. Great suggestion from someone on this NG which
had not occurred to me.

As I said before, this isn't a smart charger, just an old fashioned
transformer/rectifier.

One of the reasons I am persisting with "old, knackered" batteries from
diesel cars is that I have now had two specially purchased sealed proper
"leisure" batteries fail after something like two or three years in this
location. They don't get particularly well looked after, they are mainly
needed in the winter so don't necessarily get checked regularly in the
summer. They are connected to a couple of PIR floods but in the summer,
you never see these trigger so the batteries can get flattened by the
cats and foxes without it being obvious. I suppose I ought to add a
"battery low" circuit with a warning light, but that would steal current
and in any case ICBA. In the winter, the PIRs normally trigger when you
arrive in the evening, also you are using the non PIR lights so you know
if the batteries need charging.

It's a relatively sheltered location, otherwise I would be tempted to
put up a small windmill charger, which would probably sort everything
out with leisure batteries.