Charging a car 12v battery

Thread Starter

john2k

Joined Nov 14, 2019
127
I have a completely flat car battery as I've been unable to drive for nearly 2 months. If I disconnect the battery and bring it indoors is it possible to charge it with a AC to DC power adapter? I have one of the following power supplies that I use to test 12v things indoors https://www.ebay.co.uk/itm/190882903153

Just wondering if instead of powering something with it, will it charge the battery if I was to put the output of that onto the battery or is that a disaster? Lol just a thought lol
 

jpanhalt

Joined Jan 18, 2008
10,515
Are you within walking distance of a service station?

If your battery has been dead flat for 2 months, there is a good possibility that it is ruined. Charging it might get you started, but going somewhere in that car could get you stranded. The engine may even die while on the road.

That is why I suggest a service station. There, they can test whether the battery is ruined.
 

Ian0

Joined Aug 7, 2020
750
The first stage of charging a lead-acid is constant current, so a constant-voltage power supply would either be overloaded, shut down, or running at its current limit, any of which it might not appreciate!
If the Battery voltage was <10.8V before you disconnected it, it is probably dead. If more than that, but unable to turn over the engine it will probably recharge.
 

Thread Starter

john2k

Joined Nov 14, 2019
127
Thanks for the replies. The battery is covered by a 5 year warranty and I spoke to the shop I bought it from said it's completely dead can you charge it for me and they said it's under warranty do just bring it we will give you a new one
 

Tonyr1084

Joined Sep 24, 2015
5,238
Check out THIS thread. Synopsis: Wife left lights on for two days. Battery absolutely dead. Battery was 3 years old and I was concerned with whether it would come back or not. It did. But it's likely not going to last as long as it would have had it not been so completely drained.

Your battery - sat for two years with no charge. Probably fatal.
 

dl324

Joined Mar 30, 2015
11,894
he battery is covered by a 5 year warranty and I spoke to the shop I bought it from said it's completely dead can you charge it for me and they said it's under warranty do just bring it we will give you a new one
I'd take them up on it unless they're going to prorate for the replacement. In that case, have them test the battery to make sure it's bad.

Around here, I think they only give free replacements if the battery fails within the first year. After that, they give a prorated price for the replacement.
 

Audioguru again

Joined Oct 21, 2019
2,061
If the car was not driven for only 2 months which killed the battery then either the battery is no good or lights or something in the car was left turned on.
 

Ian0

Joined Aug 7, 2020
750
On a modern car three weeks is long enough for it not to start, due to the amount of electronics that runs continuously. (Found that out during lockdown)
But with all the fancy battery management systems cars have these days, why does it not disconnect the battery completely below 10.8V?
 

Tonyr1084

Joined Sep 24, 2015
5,238
Around here, I think they only give free replacements if the battery fails within the first year.
My "EverStart" Walmart battery has a 5 year warranty. 3 year 100% replacement. Meaning if I can prove it's less than 3 years old and bad I can replace it for free. However, this battery (in my wife's car) was already warranty replaced once.
why does it not disconnect the battery completely below 10.8V?
Even battery monitoring equipment uses some power. Had Lithium Ion batteries go bad because of the continuous monitoring.
 
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