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MG Midget and Sprite Technical - Battery blankets

Do battery blankets work?
It was -3.5c this morning and the midget was barely turning over, let alone starting. However once the temperature had risen to around 5c it started easily first time. On the basis that nothing changed other than the temperature would I be right in assuming that the battery could do with insulating?
The battery itself is from Halfords and is less than a year old, I have never had a problem with it before.
BH Harvey

It's probably not your battery but the connections, leads, earths ect. and the colder weather has just highlighted the problem

unless your battery is drained

check the distilled water level of each cell, meter the battery or put a battery charge on

don't foreget it's not just your battery that's cold at that temperatute (which isn't that low at -3.5)

all connections should be clean, secure and protected
Nigel Atkins

It could well be the battery Nigel. Battery cell performance isn't so good at very low temperatures. So whilst other factors, such as poor connections won't help, keeping the battery warmer than freezing will certainly help a lot.

How about a simple thermal jacket. Get some polystyrene sheet and enclose it.
Lawrence Slater

Should not be the batery!
Make all connections perfect and it should not be a problem.
If it is look at the charging system.

My battery had no trouble with -10 last year and that battery has just last week died on me and was by now 7 years old.
Onno K

Maybe it should not be the battery, but that doesn't mean it is not!

As I posted, battery cells aren't so efficient at lower temps, esp aqueous electrolyte batteries, just like the ones in cars.

"Cold temperature increases the internal resistance and diminishes the capacity. Batteries that would provide 100 percent capacity at 27°C (80°F) will typically deliver only 50 percent at –18°C (0°F). The capacity decrease is linear with temperature."
Lawrence Slater

-3.5 isn't that low but it will show up weaknesses which will probably be with the starting or possibly charging sytems if the battery is only 1 year old

there is a possibility that the battery could be of faulty manufacture but that would be low
Nigel Atkins

The capacity decrease is linear with temperature.

Ergo, if the temperature drops, the ability of the battery to overcome stiff oil, poor connections, etc etc is diminished!

I reckon just making the battery snug is an easy fix/test. But hey, what do I know. :)
Lawrence Slater

protecting the battery from the cold - and hot - isn't a bad idea if permanent but there’s not a lot of room usually in our cars and probably unnecessarily (I’m surprised at you suggesting such pampering)

and we did cover the cold for the rest of the car, oil ect., and that the cold highlights these things and possibly a problem

you use your car everyday did you have a battery blanket when last winter the temperatures went well below –3.5
Nigel Atkins

Summary at the bottom of this page may help -
Nigel Atkins

Why would insulating the battery help? However good the insulation, it would help for a while but eventually the temp inside the blanket will equalise with the outside temperature anyway. It would surely need some slight heat source under the insulation to be effective.

But a 1 year old battery - even one from Halfords - shouldn't have any problem at only -3.5 C Yes the output will be diminished by the cold, but not enough to make a real difference unless there are other weaknesses in the circuits, as Nigel says.

Depends on the driving done in the period before. Headlights, wipers, blower, fog lights all on? Not very much left to charge then.
Alex G Matla

heat from use of the battery and residule heat will be held for longer with insulation

would also insulate against heat from inside and outside the engine bay

how much and how effective it is is another matter

an alternator charging system and engine starting system both in good condition should give a fighting chance of keeping the battery if the journeys are not always short and subject to the stuff at the bottom of the linked page

unless you've got one of those nasty immobiliser/alarm systems fitted and don't move the car for a few weeks
Nigel Atkins

Nope Nigel, I'm lucky enough, to keep my car in an integral garage, so it's probably never colder than a few degrees above in there.

Bill wrote. "However once the temperature had risen to around 5c it started easily first time."

All that changed was the temperature.

Yup Guy, eventually the temp would drop inside any insulating material too. But it might just keep it high enough, to allow the battery capacity to remain sufficient to start the engine.

As for other conditions. You can have perfect connections, but if the battery is too cold, it won't pass sufficient current, due to it's increased internal resistance. (For this type of car battery, the internal resistance increases with the drop in temp, and that is a fact).

Now if that's the cause of Bills problem, I really have no idea, as I am not there to look and check other things.

I merely responded to his question, about thermally insulating his battery, which was prompted by his own observation, that when it was -3.5c, no start, and barely turned the engine, and when it was +5c, start no problem. :)
Lawrence Slater

what a soft southern pampered car you have :)

the 8.5 degrees increase in temperature would help the battery and car

I understand you were replying to the question

I expanded it because I think just using a blanket could cover a fault (pun intended)

my car always sits outside, the battery came with the car 4 and a half years ago, I would expect my car to start at -3.5 and the electric fan runs on mine for quite a while after ignition is off so has a motor drain to the battery (I like it this way for summer use and is no problem with winter use)
Nigel Atkins

I think whether or not insulation would help would depend how long the car was left standing, unused, at low temperature. Left long enough, it would eventually have no benefit. Unless there was some sort of background heat source under the insulation. I think though, care would be needed to allow for ventilation to disperse any hydrogen given off when in use or one could get more instant "get up and go" than wanted!

yeah, the insullation can only do so much and you might need venting extended

but protecting the battery from extremes of heat doesn't begin and end at insulation of the battery

ah, just thought, does Bill mean a powered heated blanket in which case a battery conditioner (with the unit itself protected from extreme cold perhaps if being in use doesn't keep the electronics warm enough) would probably be better
Nigel Atkins

I was considering one of the powered wrap thingies, you switch it on from inside the house half an hour before and it warms the battery.
However further research shows that these are really intended for people who have to dig their cars out of snowdrifts on a daily basis. I.e. not for a mild frost.
I shall check connections tomorrow but electrical contacts tend to be on or off in my experience, and it did start later on. My car has a battery kill switch which prevents anything from draining it.
Thanks, Ben ;)

BH Harvey

Same happened to me but the battery (just under 4 years old) needed a charge even after the temperature warmed up. Now going through the process of checking battery condition and alternator charging. Latter seems ok with 13.6 volts at 2500rpm and fan belt is at recommended tension so looking like the battery. Reading just under 13 volts an hour after charging and will check agin tomorrow to see how much it's dropped by.

Jeremy 3

>>My car has a battery kill switch<<
that would be one of the very first connections I'd check after battery lug, clamps and leads

to start a car requires a lot of battery power a poor connection alied with very cold could be enough to prevent it starting when normally it would start despite the poor connection

a weak earth that normally lets enough through could be highlighted this way

a very small amount of crud on my mate's battery lug unseen under the clamp car was enough to prevent it starting

a loose connection could also be enough

is Kent really that bad you need to use the kill switch couldn't you leave it on a use a battery conditioner rather than the minture old folks bed warmer:)
Nigel Atkins

as some one reminded me - on the car later expect near 12.6 volts
Nigel Atkins

>>>>My car has a battery kill switch
>>that would be one of the very first connections I'd check after battery lug, clamps and leads

You could always wire the starter main cable direct to the battery (means 3 fewer contacts for this cable...), and use the isolator for the rest of the circuits.

Anthony Cutler

Well, I'm not so sure that it is the battery now. It refused to start under its own power yesterday (It turned over quickly for about 6 seconds before quitting entirely), and will not catch today –despite attempts at jump starting it.
I have removed a spark plug to check for sparks, and done the same for the coil. Neither show any sign of life. Could the damp be having an effect?

BH Harvey

Damp can effect HT leads and dissy cap that need replacing but that's not the problem here as you've no spark from the coil(?)

you need to start at the begining and carry out a step by step diagnostic of the problem

in your post it suggests to me that the starter motor has stopped turning

with ignition off check the starter turns by hand, use a spanner on the square end of the starter

also check that the engine turns by hand

if both are OK then check for loose or poor connctions at starter motor and solinoid - have battery disconnected when you do these
Nigel Atkins

From the way you described the trying to start and then quitting altogether, it sounds to me like the starter is on the way out rather than the battery.

b higginson

jumping the step by step diagnostics there Bernie, and Bill put it turned over quickly for 6 seconds before stopping
Nigel Atkins

The starter is a newly added recon unit. I know that that doesn’t ensure that it is fault free but I am fairly certain that it is good (It doesn’t jam or whine, and when the car was jump started it turned the engine over well).
I have had problems like this before and found that a faulty condenser was to blame. Since then the car has been exceptionally reliable.
BH Harvey

check for loose or poor connections at starter motor and solenoid - have battery disconnected when you do these

this is jumping the gun but just to note :
>>I know that that doesn’t ensure that it is fault free . . . a faulty condenser was to blame<<
Nigel Atkins

Well i replaced the points with a spare set which I keep in the boot. This seems to have fixed the problem for now. I still don't know what drained the battery initially though, maybe just standing in the cold for a few days?
Thanks for the advice.
BH Harvey

Hi Ben,

If your battery is ok, it won't drain over a few days in the cold, unless there is an external current flowing, like leaving the side lights on or radio for example.

When you said, ---- "It turned over quickly for about 6 seconds before quitting entirely" -- what exactly did you mean?

Quitting entirely, suggests that the engine stopped turning over. Is that really what you meant?

If so, then if it "turned over quickly for about 6 seconds", and then stopped turning over, either the battery drained in 6 seconds, or the connection from the battery through to the starter motor was interupted at that point.

Apart from replacing the points, what else have you done?
Lawrence Slater

Unless you have something like clock, alarm or stereo fitted that has a permanent live feed or has gone faulty to a live drain then possibly the courtesy or boot light may be faulty and remain on or short to live for some reason

good thing you fully charged your battery, for starting and electrical problem solving a fully charged battery will help but a low charge battery will hinder

as for points ! – many modern sets of point are very poorly made, if the set you have on are not worn then clean them rather than replacing them

if you must buy points then get good quality (not always available from the big suppliers) and from a reliable source -

this is a reasonable page for battery information -

Nigel Atkins

When I worked on the North Slope in Alaska, c. 1974, all the trucks had battery blankets, water circulating heaters, and some form of oil heaters (dipstick or drain plug), I don't know how much the blanket helped, and the temps were much colder, -40f, but everyone had one.
Phil Burke

we very rarely get below 0F here, 20F is very cold here
Nigel Atkins

This thread was discussed between 16/01/2012 and 20/01/2012

MG Midget and Sprite Technical index

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