What Amp battery trickle charger to use

[Matt_T]

I have a 1990s sports car with a 65 Ah battery. It sits in my garage for several months without getting used and also has a slight drain from an old immobiliser - therefore I leave it permanently on a NOCO Genius 5 charger (5 Amp).

I now need to get a second charger as I am going to use that one for another car.

So my question is this:
The guidance I read says to use a charger that is closest to 10% of your Ah rating (so a 65 Ah battery should use approx. 6.5 Amp charger).
However there is also guidance saying "for maintaining a good battery just use a 1 Amp charger, you only need a bigger Amp charger to charge a weak or flat battery..."

So as my batteries are good, should I just buy a 1 Amp charger or should I stick to the 10% rule (which is a 5 Amp charger)?
Is there any safety issue here, ie is a low amp charger safer to leave permanently on?

Any help is welcome...

[Hawkshaw]

If it's a smart charger, the maximum amperage doesn't matter, as the charger will sense what the battery requires.

If it's an old-school "dumb" charger then 5-6 amps isn't really a trickle charge, and would be enough to recharge a flat battery overnight. That is too much to leave permanently connected. 1 amp would probably be more than enough to maintain a good battery and overcome the drain from the immobiliser. But still, not wise to leave it on all the time unless you monitor it - best to disconnect the battery from the vehicle and give it a top up charge once a month.

A smart charger is probably your best option. The only snag with these is that they won't recharge a totally flat battery, but in this case it won't have to.

[Matt_T]

Thanks Hawkshaw,

So this is the charger I have...
https://no.co/genius5

I assumed that it is safe to leave on all the time as it is a smart charger. Is that correct?

This is the 1 Amp https://no.co/genius1

Edited by Matt_T on Monday 1st December 00:32

[Griffith4ever]

Matt_T said:

Thanks Hawkshaw,

So this is the charger I have...
https://no.co/genius5

I assumed that it is safe to leave on all the time as it is a smart charger. Is that correct?

This is the 1 Amp https://no.co/genius1

Edited by Matt_T on Monday 1st December 00:32

Yes and yes. Modern ( and I mean post 70s) lead acid chargers will pretty much all drop down to a trickle charge once the battery is full. Maintenance/ trickle charge current is in the milliamps, not amps.

You'd have to buy and old, or workshop specific charger to find one that stubbornly say at 5amps, or even 1 Amp. Even then,as the battery gets full it's resistance climbs and it'll only demand what it needs. Hence old chargers with needles would show max amps and then slowly fall. You'd know when it was full as the needle would drop to minimum.

When you look at chargers they are usually three stage (some pricey ones add extra stages to lighten your wallet for no good reason). Bulk, absorption, then float. Float is also known as trickle or maintenance. There is a 4 stage, known as desulphurisation, or, recovery or repair. This pulses around 20v if your battery is at a very low voltage.

Any stages on top of these are what could be regarded as spec wars :-)

A useful tip. If you leave your car for long period, look for a charger that resumes after a power cut. Most modern ones don't.... They have a "start" button that needs to be pressed.

I use an Amazon basics charger when I go away for months at a time. It resumes after a power cut.

Edited by Griffith4ever on Monday 1st December 05:27

Edited by Griffith4ever on Monday 1st December 09:41

[Matt_T]

Thanks Griffith
The Noco Genius chargers don't need a button pressed to start, they automatically detect the type of battery and start charging.

Edited by Matt_T on Wednesday 3rd December 21:22

[AlexGSi2000]

For garaged cars I always tend to use a battery cut-off rather than leaving for months on a trickle charger.

Had batteries last 10+ years using this method.

[Griffith4ever]

AlexGSi2000 said:

For garaged cars I always tend to use a battery cut-off rather than leaving for months on a trickle charger.

Had batteries last 10+ years using this method.

That'll achieve almost the same thing.

Lead acid batteries lose charger over time, even when disconnected (slowly,). You actually extend the life of LA bateries by trickle charging them (replacing the natural lost voltage/charge). You prevent sulphation, and the natural discharge is between 3 and 5% per month, so leave it long enough and you'll damage the batteries.

The big gotcha with disconnection is cars with trackers. :-) or modern cars that get in a strop after long disconnects. Classics - makes no odds at all.

Edited by Griffith4ever on Friday 5th December 12:31