Car battery charger

It doesnt take a couple of days for the car to equalise in temperature with its surroundings.

Yes but small lead acid batteries have eyes bigger than their bellies. They are the Labradors of the battery world.

Bill

Thanks for all replies. There is a complication in that I have two cars with very different battery sizes, but I've bought a cheap 6A charger (to suit my 70Ah battery) and will try it as soon as the rain stops.

Ok, I'll bite. How would you determine the point at which you stop the bulk charging voltage of say 14.4V and go to a float voltage of 13.7V or so.

Hint, if you want your battery to last you won't want to keep it at

That is another issue.

That depends on whether you want any electrolyte left in your battery after an extended charge.

it's bs to try to persuade people with more money to hand over more of that money for a larger charger that they don't need.

Lead acids charge constant voltage, so any size at all can be charged by any lead acid charger.

However... if you make a habit of using said charger, you should use one that matches the type of lead acid. There are differing voltages for flooded starter batts versus SLA, and the phosphoric acid ones are a bit different again.

yes

that isn't a need. An old 4A charger will soon get you going. Sure, it takes longer with a diesel.

Not really, you can start a typical petrol car from a small battery. Capacity fitted is chosen for other reasons.

This is a half truth promoted by charger mfrs to make their chargers sound better. Those 2 phases are the same thing from the charger's pov, ie V and i are both limited. V is limited to suit battery chemistry, i is limited to avoid charger failure.

Dumb as a rock chargers are not safe. If you stop them before the thing is fully charged, and only use them occasionally, no worries. Ignore those and don't be surprised if your battery gets ruined. But useful for discharged batteries, which smart chargers won't charge!

Not many chargers have temp compensation, they're expensive, and for most users thus not the best option.

Because although the cranking current is very high the duration is very short. 120A for 30 seconds is 1Ah.

Bill

The cheap charger I bought wouldn't deliver more than 1A to either of my batteries. (I measured it with a separate ammeter; it didn't have a built-in ammeter, which I regret.)

I had hoped it would deliver the rated current of 6A so as to speed up the charging, and then switch itself off when the battery was full; but apparently this is not how it works.

Many have a relay on their output, coil fed from the battery via a diode, to prevent wrong connection. Which means a very flat battery won't pull it in. Jumping the battery with a good one and the charger connected will persuade it to connect, and you can remove the jump battery immediately. Of course a battery which as been that flat may never recover.

I have a conventional Halfords charger - large and heavy. Claims 11 amps on the front. Takes longer to charge a battery than the smart Lidl one I have too - which only claims under 4 amps. And is a fraction of the size. And cost.