PaulRainbow
Well-Known Member
Despite the multitude of replies on here for solutions that say otherwise !!!
Charging a 12v battery from another 12v battery?
- Thread starter Skylark
- Start date
B27
Well-Known Member
It's a difficult question to know how quickly the alarm will kill the battery.Thanks @B27 I planned to simply remove the battery (and one of the road wheels) for security. Easy then to top-up the battery at home whenever I remember. This plan was scuppered by the Insurer mandating that I get an alarm fitted. Hence my question
It’s not worth the risk of ignoring the insurer.
Temperature swings can speed up self-discharge I believe.
A month can be long enough for a battery to lose charge even with no drain.
I'm wondering if the alarm could be powered from something other than the car's battery, but I can only think of expensive Lithium primary cells.
Another avenue to explore would be some sort of GSM/SMS alarm to send you a text when the car battery drops below a certain level? There's various on ebay, not sure if anything could text you at say 12.4V without adding extra circuitry?
But these things start below £50.
I looked into this seriously about 15 years ago, hopefully the right thing is out there, it can't be a unique need?
PaulRainbow
Well-Known Member
The biggest hurdle is the time taken to charge the battery from another battery. It's eminently possible, but would likely take some time. Swapping the battery once a month seems like a cheap and simple option to me. No need to refit battery clamps etc, so should be a quick enough job.
penberth3
Well-Known Member
Alternatively, move to a low crime area
There's no such place! If somebody wants something they'll find it and take it. And the missing wheel idea won't stop them.
Alicatt
Well-Known Member
If it is the car I'm thinking on, my brother used to leave his at Aberdeen airport for up to 3 weeks at a time without problems while he was offshore, however he did not have a tracker type of alarm just an immobiliser, his friend's BMW 3 series would go flat in less than 2 weeks but it has a whole slew of electronics in it compared with the one I'm thinking of.
One of my cars has a proprietary alarm system on it that reports back to a central station, they will call me if the battery drops below a certain level.
Aja
Well-Known Member
Deleted.....
William_H
Well-Known Member
Assuming the OP visits the lock up occasionally with another car. The simple answer is to use jumper leads to charge the stored car battery from the visiting car with engine left running. ie battery charged by visiting car. An amp meter in jump leads might give you an idea of just how much charge is going in.
If OP wants to decant charge from one battery to another something like this would be ideal. But would still take some time max 5A.https://www.ebay.com/itm/175521285624?hash=item28dde245f8:g:hasAAOSwrPtjjwYE&amdata=enc%3AAQAIAAAA4Lryd53PEsJewe3F4htlPWhH6gEjXANzgripTt8jHVnbkMMxmi1WnYh4HxjQ9fnMe14air%2FwakZEO99nAcLEMi0yEQEck1ziicbPKQSUqpwwH7Vk8bIpq%2BJOMh6QRzLutV8%2BnP9vCah%2F3rz48k8uuFvYmx0JFRecSequBceYULHg8ZiErGoCuYNqqT%2B6r2gl9EnJ4de8amu5ETkZcchfCnr0F%2FGcHt%2B4JUV%2FmZzGOGnvY3mZkpFB3enVZlm8RgVu5oSj3krKfXhON0gb0idh2HYYCQF%2ByWfWJogEo6tRGcZQ%7Ctkp%3ABFBMsMzskf9i
ol'will
If OP wants to decant charge from one battery to another something like this would be ideal. But would still take some time max 5A.https://www.ebay.com/itm/175521285624?hash=item28dde245f8:g:hasAAOSwrPtjjwYE&amdata=enc%3AAQAIAAAA4Lryd53PEsJewe3F4htlPWhH6gEjXANzgripTt8jHVnbkMMxmi1WnYh4HxjQ9fnMe14air%2FwakZEO99nAcLEMi0yEQEck1ziicbPKQSUqpwwH7Vk8bIpq%2BJOMh6QRzLutV8%2BnP9vCah%2F3rz48k8uuFvYmx0JFRecSequBceYULHg8ZiErGoCuYNqqT%2B6r2gl9EnJ4de8amu5ETkZcchfCnr0F%2FGcHt%2B4JUV%2FmZzGOGnvY3mZkpFB3enVZlm8RgVu5oSj3krKfXhON0gb0idh2HYYCQF%2ByWfWJogEo6tRGcZQ%7Ctkp%3ABFBMsMzskf9i
ol'will
KevinV
Well-Known Member
I'm amazed that any insurer still requires the fitment of an alarm - everyone ignores them so they're pointless. An immobiliser is a whole different matter of course.
Could you simply wire the alarm via a low voltage cut-out, such as used for boat fridges? Then you have indeed fitted it, and activated it, as per the insurers requirement
Could you simply wire the alarm via a low voltage cut-out, such as used for boat fridges? Then you have indeed fitted it, and activated it, as per the insurers requirement
Kelpie
Well-Known Member
Buy two car batteries and a set of jump leads. Leave the car's own battery as is, and hook up one of the new batteries in parallel. Every month, swap for a fresh one. Will take a few seconds and you don't even need to open the bonnet. No need to hang around waiting on a charger.
Skylark
Well-Known Member
It’s worth a bob or two but I wouldn’t describe it as exceptional.
I have two of these cars. I keep one in my home garage. It has a Thatcham Cat 1 alarm and immobiliser. The other one, the subject of this thread, currently does not have an alarm and I’ve recently moved it to a lock-up. Both cars are on one policy. The insurer is perfectly happy with the move but they have mandated that it must have a Cat 1 alarm/immobiliser fitted.
Thanks for the additional comments @B27 I’m having the same alarm fitted to the grey car (lock-up) as I already have fitted to my black one (home garage) so I have long experience that a monthly top-up charge over the winter months should be fine.
Thanks @PaulRainbow Time to charge shouldn’t be an issue. Changing battery once per month is also a viable option.
Thanks @Kelpie that sounds like a simple solution, I’d be happier if I could do this with a bit of control.
The lock-up is very close to home so I visit regularly.
Thanks to everyone for additional comments, many made me smile.
Refueler
Well-Known Member
See my post ... he certainly can use one battery to charge another ....
Refueler
Well-Known Member
He already has a charger that can work from one battery to another ....
TBH - I rather like the idea by another ... have jump leads and a parallel battery outside car that can be swapped easily ...
My last cars over last 20yrs - all have been a pain for more than 2weeks standing ... not only batterys running down due electronics on board ... but my 24v had hydraulic valves .... if car left more than a week - it took the on board + a second battery to get system fired up again ...
Graham376
Well-Known Member
That's what we used to do with old car when away sailing. When reconnected after 5-6 months battery would still start the car. Unfortunately, can't do that with newer modern car so now leave it on maintenance charge with CTEC charger.
billskip
Well-Known Member
What actually activates the alarm? Door ? Motion? Noise? ...if it's only door then it's very simple to put in a latching relay and you can then isolate the system from the battery until it is activated.....
Alex_Blackwood
Well-Known Member
Wasn't that the original query Charging one battery from another???
Kelpie
Well-Known Member
Not exactly. OP was going to buy one more battery and swap them, I think. I suggested buying two more batteries instead.Wasn't that the original query Charging one battery from another???
Although the title of the thread does suggest that he was thinking if doing that anyway?
The key thing about buying two batteries is that you leave the fresh battery in parallel for long enough to equalise voltage and therefore fully charge the car's own battery. Which would probably take days, so only viable if you can leave it set up like that.
Refueler
Well-Known Member
The only part to be aware of with the parallel battery - is the diminishing return ...
At first its with car and second battery fully or near full charged. Both disharge slowly ... this is the longest time before need to change. Then change second battery - this will immediately commence equalising with cars battery ... meaning that now - the time before change of second battery is shorter. If its left for similar time as first change ... the two will be lower state when changed ... etc etc.
Whats needed is to time to charge state for first and second change. Then keep to second result - to avoid that diminishing return factor.
Some may think it not much concern ... but after a few changes - if not taken into account - can in fact lead to seriously discharged batterys.
At first its with car and second battery fully or near full charged. Both disharge slowly ... this is the longest time before need to change. Then change second battery - this will immediately commence equalising with cars battery ... meaning that now - the time before change of second battery is shorter. If its left for similar time as first change ... the two will be lower state when changed ... etc etc.
Whats needed is to time to charge state for first and second change. Then keep to second result - to avoid that diminishing return factor.
Some may think it not much concern ... but after a few changes - if not taken into account - can in fact lead to seriously discharged batterys.
PaulRainbow
Well-Known Member
This isn't possible. To fully charge the car battery, the donor battery would need have a terminal voltage of 14v ish. The best that would happen is that the two batteries would equalise, that's subject to post #37
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PaulRainbow
Well-Known Member
How about merging a couple of the suggestions in the thread....
Buy two batteries and leave the car battery in situ. Fit a small DC-DC converter in an enclosure (bearing in min possible over heating) and have two pairs of cables, with croc clip on them, one pair would be the converter "in", connected to the donor battery, the other would be the controller "out", going to the car battery. Just swap the donor battery regularly and the car battery will always be fully charge (assuming you don't leave it too long between swaps.
Buy two batteries and leave the car battery in situ. Fit a small DC-DC converter in an enclosure (bearing in min possible over heating) and have two pairs of cables, with croc clip on them, one pair would be the converter "in", connected to the donor battery, the other would be the controller "out", going to the car battery. Just swap the donor battery regularly and the car battery will always be fully charge (assuming you don't leave it too long between swaps.