New Battery - Old Battery

[The Mad Monk]

I fitted a new battery in October - just to be on the safe side really, with Winter just round the corner.

Put the old one in the garage. Today I thought I would put it on charge, you never know, it might be handy as a backup? Connected up the charger. Inside a couple of minutes it was showing fully charged and had switched to maintenance. 'Strange' thought I, so I unplugged it, left it a short while and plugged it in again, within a few seconds it had switched from 'charge' to 'maintain'.

Either the battery is so flat that it won't take a charge, or it's so fully charged that it won't take a charge. Neither of which make sense to me.

Any ideas, please?

[SteveR1979]

Battery should be able to hold its charge for months if there is nothing wrong with it.
You said yourself there is nothing wrong with it, so seems perfectly plausible

[The Mad Monk]

SteveR1979 said:

Battery should be able to hold its charge for months if there is nothing wrong with it.
You said yourself there is nothing wrong with it, so seems perfectly plausible

Is there a simple (safe) way to discharge the battery a bit?

[Desiderata]

The Mad Monk said:

Is there a simple (safe) way to discharge the battery a bit?

Set of jump leads and anything that needs some current.

[paradigital]

The Mad Monk said:

Is there a simple (safe) way to discharge the battery a bit?

Literally anything that provides a load. A couple of spare headlight bulbs perhaps.

[A1VDY]

Once fully charged a pulse/smart charger (as you have) will automatically go to 'maintenance'.
It doesn't mean that as soon as it switches over its then putting charge into the battery, this will only happen if the charger detects any slight discharge.
Theres nothing wrong with either your battery or charger..

[mikeiow]

Had this advice from a battery manufacturer some years back. Despite sounding somewhat unlikely, I can tell you it has worked 2 or 3 times for me on a couple of cars with apparently dead batteries:

Please try the following to re-charge your battery:

1. Connect flat battery to any other battery with jump leads
2. Leave for 10 mins and then connect charger to flat battery at same time.
3. Turn on charger and charge like this for 1 hour.
4. Then take off jump leads and charge battery normally with charger for minimum of 12 hours.

This will then bring the battery up to 12.73v (100% Capacity)

[A1VDY]

mikeiow said:

Had this advice from a battery manufacturer some years back. Despite sounding somewhat unlikely, I can tell you it has worked 2 or 3 times for me on a couple of cars with apparently dead batteries:

Please try the following to re-charge your battery:

1. Connect flat battery to any other battery with jump leads
2. Leave for 10 mins and then connect charger to flat battery at same time.
3. Turn on charger and charge like this for 1 hour.
4. Then take off jump leads and charge battery normally with charger for minimum of 12 hours.

This will then bring the battery up to 12.73v (100% Capacity)

This is correct but a pulse/smart charger will do this type of charging for you.

[GreenV8S]

That suggests the battery has come up to the expected voltage so the charger decided it is fully charged.

It shows that the battery doesn't have any dead cells but doesn't tell you much else about the charge capacity or current capacity of the battery. The only way to measure those would involve putting it under load. But if the battery was working fine as far as you know when it was removed, it's probably still fine now.

[The Mad Monk]

The thing that I struggle to understand is why, if the battery was left untouched for 10 weeks, it has lost so little charge?

Perhaps I will see if I can discharge it a bit tomorrow, then see how long it takes to get up to fully charged. Would a four year old battery really hold full charge for 10 weeks?

Edited by The Mad Monk on Saturday 26th December 20:20

[Twig62]

I don't understand why are you worrying about this !

[The Mad Monk]

Twig62 said:

I don't understand why are you worrying about this !

I think it's because I've got nothing much else to worry about, I suppose. It is Christmas, after all!

Actually, if the battery is sound I will keep it, it it's duff, I will chuck it away.

I am grateful to everyone for their replies.

[Evoluzione]

Twig62 said:

I don't understand why are you worrying about this !

Yes, along with WTF did you throw it out?
The battery on my van is 10yrs old and still works fine, even the puny thing on my car did 7yrs before I changed it.

[mikeiow]

A1VDY said:

This is correct but a pulse/smart charger will do this type of charging for you.

Well, one might think that, but my smart charger failed to save those cars (keeps the Figaro ticking over normally).....whereas that procedure just worked!

[A1VDY]

mikeiow said:

A1VDY said:

This is correct but a pulse/smart charger will do this type of charging for you.

Well, one might think that, but my smart charger failed to save those cars (keeps the Figaro ticking over normally).....whereas that procedure just worked!

I'll be the first to agree, new technology won't always be the best. Your old school trick is well versed and obviously worked.
An old school auto electrician I knew (now sadly gone) with a completely dead battery used to stick 60plus amps into it for 30 mins to remove residue from the plates (virtually cook it!) before trickle charging it. Not sure if that was really successful, seemed a bit brutal to me..

[Hereward]

Ignore what the charger does and ignore the voltage across the terminals. A sick battery can still show >12.4V and fool a smart charger.

You need a battery health tester to establish the Cold-Cranking Amps (CCA) of the battery to determine if it's truly healthy or not.