What would you do?

Euphony

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Hi all,
When my MH went in for her MOT last month the guy said that "my battery was lethargic in turning over the engine and might only last a few more months, it's definitely on it's way out". I hasten to add he didn't try to sell me one, it was simply a heads-up.
I bought a very good new battery a week later from Eurocarparts but I haven't installed it yet. The engine is definitely turning over noticably more slowly now (it is so slow you'd think there was no way it is going to start it) but it will start within 4 or 5 seconds as opposed to the previously immediate start.

My question is: Should I just install it now or wait until the better weather and not have it sitting in the current freezing conditions?
 
Last edited:
Sep 27, 2007
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When I started our m/h today, it too was slow with the turnover, it started on the third try.......I put this down to the -5* temp for the last two mornings. On checking the battery voltage after it had stood for a couple of hours, the voltage reading was 12.4.

I would wait for the cold snap to pass before changing.

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Mikey RV

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Why wait if you have been told it’s on it’s way out change it now. Better than being stuck somewhere and changing it then.
 

Charlie

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Get it drop tested by a battery supplier. This should not cost and will give an indication of the battery’s condition.

Or just replace it...

EDIT.
Sorry just re read the OP....

Get your new one fitted. Battery’s do not like sitting unused even if topped up by a charger so having it sitting doing nothing is detrimental to it..

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Derbyshire wanderer

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A lazy battery should be changed as soon as practicable because as the voltage drops the current increases causing extra load on both the wiring and the solenoid contacts.
Rarely will it have a noticeable effect but can lead to premature starter motor failure.
 
Aug 6, 2013
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A lazy battery should be changed as soon as practicable because as the voltage drops the current increases causing extra load on both the wiring and the solenoid contacts.
Rarely will it have a noticeable effect but can lead to premature starter motor failure.
Ohms Law would suggest that is not the case? The starter electrical resistance is a constant (it isn't really because it's a motor but for this purpose we'll assume it is) so if the voltage supplied to it drops so will the current.
 

Derbyshire wanderer

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Ohms Law would suggest that is not the case? The starter electrical resistance is a constant (it isn't really because it's a motor but for this purpose we'll assume it is) so if the voltage supplied to it drops so will the current.
What you haven’t considered is the load in watts. For simplicity an equivalent 24v stater motor draws half the current.
As the load increases, the demand does so any lower voltage means higher current draw.

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Jan 19, 2014
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What you haven’t considered is the load in watts. For simplicity an equivalent 24v stater motor draws half the current.
As the load increases, the demand does so any lower voltage means higher current draw.
No, with lower voltage the wattage consumed will be less... To maintain the same wattage with a lower voltage the current would be higher.
Imagine connecting a 1.5v power scource to a starter motor, with your thinking the current draw would be massive, in reality nothing much would happen.
 
Apr 27, 2016
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For a range of different motors with the same wattage designed for different voltages, the current does indeed increase as the design voltage reduces.

For any individual example of a motor, the current will reduce as the voltage decreases. The wattage is not fixed but depends on the voltage and current.

In fact if the voltage decreases by 10%, the wattage will decrease by about 20%.

There are some electronic devices, like laptop chargers, that will automatically increase the current to compensate for a lower voltage, and maintain a constant wattage output. Dumb devices like lights, heaters and motors will not do this.
 
Jan 19, 2014
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Voltage regulators on LEDs do it. It's weird to see the current go up as you turn the supply voltage down. :rolleyes:

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Derbyshire wanderer

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No, with lower voltage the wattage consumed will be less... To maintain the same wattage with a lower voltage the current would be higher.
Imagine connecting a 1.5v power scource to a starter motor, with your thinking the current draw would be massive, in reality nothing much would happen.
I agree that a very low voltage will not work but we are talking about a 12v battery that is losing voltage under load.
As the voltage reduces the current increases as long as the load is the same.
 
Apr 27, 2016
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I agree that a very low voltage will not work but we are talking about a 12v battery that is losing voltage under load.
As the voltage reduces the current increases as long as the load is the same.

That's a different effect. As the current increases, the battery is unable to maintain the voltage, so the voltage reduces, typically from 12 volts to maybe 8 volts.

If by some miracle the battery managed to maintain its voltage at 12 volts, the current would be much higher than the current at 8 volts. The motor would probably overheat and burn out.

Starter motors are designed to take the voltage drop into account, so 8 volts is exactly what they are expecting.

Both the current (amps) and the load (watts) at 8 volts are much reduced from the current and load if the battery had managed to maintain 12 volts.

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OP
Euphony

Euphony

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I love all the contradictory posts about Watts, Ohm’s Law, current draw, electrical resistance and Volts. I don’t understand a word of any of them but they are most entertaining!
Me neither, I was only asking would you/wouldn’t you.

I changed it over this morning and it’s great.(y)

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Oct 7, 2013
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Get it drop tested by a battery supplier. This should not cost and will give an indication of the battery’s condition.

.

Last time I did a drop test I got to 1.6metres before the casing shattered, but it still wouldn’t start the engine.:whistle:
 
OP
Euphony

Euphony

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Nov 9, 2016
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Hi All,
Thanks for you’re varied opinions and input, I changed to the new battery this morning, “ job’s a good’un”.
 
D

DL42846

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I would change it as the guarantee is running, Also it will enable you to check to see if it is the battery or not something like a bad earth connection or something along those lines. Could even be the starter motor on the blink. You could always test the battery with a volt meter.

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OP
Euphony

Euphony

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Nov 9, 2016
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3 years of weekending with the odd month here and there.
I would change it as the guarantee is running, Also it will enable you to check to see if it is the battery or not something like a bad earth connection or something along those lines. Could even be the starter motor on the blink. You could always test the battery with a volt meter.
I changed it this morning as per previous post, it’s great.
 
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