I've SORNed my car as I'm not going to be able to drive it for a couple of months. No doubt the battery will eventually need a charge but do I really have to disconnect it as current [pun not intended] advice seems to indicate? If I do, I will, no doubt, have a whole lot of setting up to do on the various electronics.
It's many moons since I last charged a car battery and at that time I just clamped the charger leads on and let it get on with it.
That's what I do.
No. My 'race' car sits for months in the garage with its battery connected to the car and a 'el cheapo' float charger from eBay. The latter was an experiment, following the 'el expensivo' float charger (an AirFlow one, IIRC) that went mad and boiled the lawn mower battery dry. Asking around, lots of other people recommended other expensive chargers, for prices that I thought were nonsense (£50+), so I bought 2 of these;
The car's been on one of them for 3 months now, and has been fine. The other one awaits me buying a new lawn mower battery.
P.S. re-reading your posting, the reason people suggest disconnecting the battery is that most modern cars have a substantial current drain even when switched off (I've measured it at several hundred milliamperes). This will rapidly flatten and then ruin a car battery. Which is why I use a float/trickle charger (sometimes called a "battery conditioner").
I often don't touch the kitcar (or several motorbikes) for many months and they all normally start ok ... so it very much depends on the parastatic load.
*Eventually* yes. ;-)
If you do then you can probably guarantee (depending on the state of charge of battery on disconnection and it's general condition) it should be ok when needed next.
Radio code, what else OOI?
If the car has a reasonable parastatic load (alarm etc) you will need to do something so what you do (charge as is or with the battery disconnected) is down to how easy it is to reset said 'electronics'?
Cheers, T i m
Sorry, 'parasitic' ...
Cheers, T i m
Though they do progressively shutdown more and more systems over the course of hours/days/weeks.
With a decent, modern, well-regulated charger, it isn't an issue. With an old, poorly regulated, poorly rectified one I'd be more cautious.
CTEK ones are great, and designed to be used like this, and you can get leads you permanently connect to the car that end in a socket that mates with the charger; I regularly charge the battery on my other half's car like this (she doesn't use it much).
That's exactly what I would have suggested, always assuming you have mains accessible to the parking place. If not, remove battery and either leave it on a trickle charger, or on an ordinary one for a few hours every month or so.
With a half decent modern ordinary charger, just leave the battery connected. The problem can occur with a commercial fast charger - the type that can start a car with a flat battery immediately. Which might chuck out enough volts to damage electronics.
I have one of those excellent 13 quid Lidl chargers installed in the old car and hard wired to a fusebox. With a waterproof mains connector under the bumper. Allowing the battery to be charged with the car still secure.
If you take a fairly normal (large) 75 amp hour battery, a drain of 1 amp would flatten it in 3 days. Pro rata for a lower current. And it would fail to start before the battery was totally flat.
Most cars can last about 3 weeks without being run. Which would suggest a quiescent current draw of rather under 100mA. But it may be higher until the electrics finally go to sleep.
Quiescent. It is necessary ;-)
Assuming the battery isn't knackered, the internal impedance will stop most chargers doing anything silly. Excepting a very powerful garage type one.
You need to be aware that SLI LA batteries aren't designed to cope with continuous float charging for month after month after month periods at the classic (and seemingly more benign) 13.8v level. Six months seemed to be the point where such 'gentle float charging' would ruin them (a bunch of four connected to an APC SmartUPS2000 2KVA/1500W rated UPS... Twice!).
Another problem is the lack of stirring of the electrolyte to prevent stratification. Surprisingly, the apparently rough treatment meted out by the alternator's 14.0 to 14.2 float charging and the vibrations and accelerations of a moving vehicle all conspire to maintain the battery in peak condition. The high voltage 'float charging' under these normal conditions of use, rarely top more than 3 or 4 hours per day, unlike the unremitting regime of a permanently connected 13.8v battery charger.
You really only need to stop the battery voltage dipping below the 12.7v mark so a basic 13.8v constant voltage charger can be used with a 6A or higher rated silicon diode to drop the charging voltage down to the 13.1v mark if you can't get hold of a 13.5v constant voltage charger.
Alternatively, a "Smart charger" that can boost the battery voltage to
14v for half an hour every 24 hours that just monitors the battery voltage during the other 23.5 hours of the day to make sure it doesn't drop below 12.6v in between these brief bursts of freshening charges is probably the best you can do to maintain the battery in a healthy state.You won't be able to prevent stratification of the electrolyte unless you're prepared to remove the battery onto a stirring platform or else are prepared to set the burst charge rate to 15 or 16 volts to induce gassing and the need to top up with distilled water every other week or so.
Probably the simplest "Fit 'n' Forget" solution is to use a standard
13.8v charger designed to maintain SLA batteries which can tolerate this constant voltage float charging regimen (even better if 13.5v is used) with a simple silicon diode volt dropper to hold the battery at a constant 13.1v for the duration.An alternatively "Cheap 'n' Cheerful" solution, if you already have a simple unregulated transformer/rectifier battery charger to hand, is to invest in a basic mechanical timer switch to put in line with the old fashioned charger set up to give it half an hour per day's boosting charge. The important point in all of this, being the avoidance of an unrelenting 13.8v float charging regime over a period of 5 or more months at a time.
And they are on sale again in Lidl today
-Can you not trickle charge it for a few hours a day on a cheapo timer? You are right its probably going to be very very flat and also I feel that vehicles engines should be turned over pretty regularly as well. Brian
The main source of current drain is probably the radio. When you switch it off, you're only turning off the amplifier, the tuning bits, etc, are still powered. Alarms also take a bit of power.
Good point ... assuming it is actually being used (like an alarm as I'm assuming an immobiliser would still be 'working' anyway? ). ;-)
Cheers, T i m
On a modern car you might be amazed how much is powered up all the time. My radio retains its station memory etc even if totally powered down.
Don't forget the remote central locking. Requires a receiver of some sort powered up at all times. Then there's likely one of those nice units that fade the interior lights up and down when you open a door. Same sort of thing.
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