How Long Should it Take a New Alarm Battery to Charge?

[Eugene's DIY Den]

I’m after putting a new 12 V, 7 AH lead acid  battery into my alarm panel. Off load voltage was 12.9 V at the battery terminals before fitting. A fully charged 12 V battery should read around 12.8 V. When I did a load test, with the panel and sensors pulling 0.55 A, the voltage eventually dropped to 12.0 V before I stopped the test after a few minutes (the voltage fell faster at first). Float charge voltage for a lead acid battery (and from a panel) is typically 13.8 V. So just wondering since the battery isn't charged in a three state mode by a panel like a normal charger would charge it (constant current, constant voltage and then trickle maintenance charge), how long typically does it take a new battery to fully charge? I've seen figures of 24 to 48 hours mentioned.

Edited April 26 by Eugene's DIY Den

[Eugene's DIY Den]

I'll see if I can find some charge/discharge curves. Presumably if the battery was sitting on a shelf in a store, it may have self-discharged somewhat. Not sure what the self-discharge rate is for lead acid, but 12.9 V would have indicated that it was fully charged, but maybe not. I guess there's some variability. The panel is trickle charging it at 22 mA. That figure was 38 mA for the 6 year old battery (which I thought was a Yuasa, but it was an Interlogix. I presume these are just badged and there are a limited number of battery manufacturers)

Edited April 26 by Eugene's DIY Den

[ian.cant]

Two things of note here, if your panel is pulling over half an amp quiescent that seems quite high to me and also if your new battery is dropping to 12v under load I would suggest its not a good battery.

[PeterJames]

13 hours ago, ian.cant said:

Two things of note here, if your panel is pulling over half an amp quiescent that seems quite high to me and also if your new battery is dropping to 12v under load I would suggest its not a good battery.

He said 55mA not 550mA

[ian.cant]

9 hours ago, PeterJames said:

He said 55mA not 550mA

 

23 hours ago, Eugene's DIY Den said:

with the panel and sensors pulling 0.55 A,

Thats half an amp in my book

[james.wilson]

It should recharge within 24 hours. 

Also needs to, to comply

[Eugene's DIY Den]

So I left it for 3 days and performed a longer test this time. After ten minutes pulling 0.55 A, voltage stabilised at 11.9 V. (it was at 11.9 V after around 2 minutes).

[Eugene's DIY Den]

On 26/04/2025 at 22:13, ian.cant said:

Two things of note here, if your panel is pulling over half an amp quiescent that seems quite high to me and also if your new battery is dropping to 12v under load I would suggest its not a good battery.

I've got 5 PIRs (older ones so current consumption might be higher than newer ones). Also 6 shock sensors, a wired bell and two wired keypads. That's 14 devices (and there's also the panel itself that has to be powered), so if they're pulled a few tens of milliamps, it could add up. I'd have to check all the specs to see what the current consumption is.

[Eugene's DIY Den]

if the float charge is only 22 mA, it could take more than 24 to fully charge the battery, depending on its initial charge state. It is a 7 Ah battery.

[Eugene's DIY Den]

So I'm thinking this low measurement could be due to voltage drop on the connecting leads (which could amount to a few tenths of a volt at that current). The panel will only measure voltage at the board during a load test.. Next step is to check voltage at the actual terminals of the battery.