Car battery during lockdown

ChemistryTeacher

With modern battery chargers there is very little damage you can do to the car when charging with everything still connected. Any ripple voltage is smoothed out by the massive battery (a large buffer). Never connect a battery charger to the car without the battery. If you do disconnect the battery then you run the risk of a voltage spike when reconnecting, or electronics losing settings or reporting disconnection faults etc. to the ECU.
Alternators charge batteries pretty quickly these days, so it usually only takes about 30s for the starter-motor current to be replaced on the battery (assuming a normal first start). Alternators don’t charge differently at different engine speeds (hence the name). Longer starts will require more running charge time commensurately. However, repeated cold starts increase engine wear etc. so best to avoid if possible.
To answer the original question, the best thing you can do is to leave a smart charger connected to the battery (direct + to + and - to -) if it’s going to be left unused for weeks. If only days then if it’s a healthy battery then no problem.
Even the lowest power smart charger (Ctek are a very reputable brand - can be found easily online) will keep a healthy battery topped up (but to charge a large battery from dead you’ll need a higher power charger), so if it’s a healthy battery perhaps just get a cheap one for now. Lead-acid batteries also have a finite life span (depending on engine size etc.). If you get more than 8 years out of one then you can consider yourself lucky. Yes, a lot of factors to consider, but if the car normally starts normally then you’ll probably do best to just get a cheap smart charger and leave it hooked up. If the battery’s in the boot (rather than under the bonnet) then it’s even safer to leave hooked up in all weather since you should be able to weather-proof the extension lead by carefully shutting the boot gently over the mains cable.

chrisw

Typical. Just got in wife's car to nip to the shops and the battery's dead. I've stuck it on charge for now but it's 10 years old and felt weak for a while. So I suspect a new one will be on the cards shortly.

tedted

ChemistryTeacher said:

With modern battery chargers there is very little damage you can do to the car when charging with everything still connected. Any ripple voltage is smoothed out by the massive battery (a large buffer). Never connect a battery charger to the car without the battery. If you do disconnect the battery then you run the risk of a voltage spike when reconnecting, or electronics losing settings or reporting disconnection faults etc. to the ECU.
Alternators charge batteries pretty quickly these days, so it usually only takes about 30s for the starter-motor current to be replaced on the battery (assuming a normal first start). Alternators don’t charge differently at different engine speeds (hence the name). Longer starts will require more running charge time commensurately. However, repeated cold starts increase engine wear etc. so best to avoid if possible.
To answer the original question, the best thing you can do is to leave a smart charger connected to the battery (direct + to + and - to -) if it’s going to be left unused for weeks. If only days then if it’s a healthy battery then no problem.
Even the lowest power smart charger (Ctek are a very reputable brand - can be found easily online) will keep a healthy battery topped up (but to charge a large battery from dead you’ll need a higher power charger), so if it’s a healthy battery perhaps just get a cheap one for now. Lead-acid batteries also have a finite life span (depending on engine size etc.). If you get more than 8 years out of one then you can consider yourself lucky. Yes, a lot of factors to consider, but if the car normally starts normally then you’ll probably do best to just get a cheap smart charger and leave it hooked up. If the battery’s in the boot (rather than under the bonnet) then it’s even safer to leave hooked up in all weather since you should be able to weather-proof the extension lead by carefully shutting the boot gently over the mains cable.

a lot of the above is nowhere near right.

omendata

Just disconnect the battery +ve RED lead - seemples!

AdrianC

omendata said:

Just disconnect the battery +ve RED lead - seemples!

Nope!

Apart from problems with memories, with alarm, with calibrations for various things... you ALWAYS remove the earth lead first. That way, if you touch the spanner against metalwork while slackening the clamp, you don't short.

neilmcl

As above, always disconnect negative lead first then live and when fitting do this in reverse (is, live then negative).

TychoTMA

tedted said:

a lot of the above is nowhere near right.

It is extraordinary how there comes to be so many experts on lead acid batteries, but how contradictory their pronouncements  are.
It seems to me that it would be a good idea if the driving test included some practical test on basic car car, so we're talking battery, fluids, tyre and lights. I was in a friends car when the alarm went off to say one or more of his tyres were below pressure. His reaction was, "Well, it was only serviced a couple of months ago" 

They just put the MoT requirement on hold while stressing that every driver must maintain his car in a safe condition. Well, in a situation where many drivers have no idea about the most basic aspects of car care, that's another good reason to stay at home.

[Deleted User]

I've been going out for a drive by myself every day. Believe it or not it's still legal to and if any overzealous cop stops me they will be told so.

prowla

I try and do a few miles trip on the weekend.

AdrianC

TychoTMA said:

It seems to me that it would be a good idea if the driving test included some practical test on basic car car, so we're talking battery, fluids, tyre and lights.

It's been in the driving test for the last 17 years.