charging auxiliary (alarm) 12V battery

[JonE]

does any one run an auxiliary battery for other 12V items on your car?
I bought a low Ah Lucas alarm battery new from Tayna and have recently popped it on the LidL charger. It doesnt do what the car batteries do and ramp up the 4 bar levels in the display. It has just risen to 12.8V and no visible bars. No further rise in a 24 h period.
Just wondered if that sounds correct?

["Slack Alice" Simon]

I always thought a 12 volt battery should show 14.4 when fully charged.

That is the old "lead acid" type.


Reading the Forum I discover that there are now batteries with different internal compositions, which have different end point voltages when charged.


So: maybe some internet research needed?   Do you know what kind of battery it is?

[JonE]

one of these - about a tenner and hopefully will run an aux pump for 3 hours!

https://www.tayna.co.uk/industrial-batte.../lsla5-12/

[Parazine]

I always thought a 12 volt battery should show 14.4 when fully charged.

That is the old "lead acid" type.


Reading the Forum I discover that there are now batteries with different internal compositions, which have different end point voltages when charged.


So: maybe some internet research needed?   Do you know what kind of battery it is?

A 12V battery, fully charged is 12.6 - 12.8 V depending on temperature.
14.4V is the voltage used to "bulk charge" the battery, which will always promote current flow through it. Excess current will overcharge the battery and will lead to destruction eventually, so modern "smart" chargers will raise the voltage to 14.6 for the bulk charge period, then, when the current levels out, switch to "float charge" at 12.8V which will maintain a few mA through the battery and can be maintained indefinitely without degradation.

[Robert Leigh]

Jon
The 5Ah rating of your battery relates to a 20 hour discharge period, for which the load would be 0.25 amps. Being an alarm battery it would usually be maintenance charged from the alarm system, but on power failure it would keep the alarm working for 20 hours if it drew 0.25 amps. I believe electric pumps for cars draw about 4 amps, so simple arithmetic gives 1.25 hours running from a fully charged battery, but in practice it would probably probably be less than this because the battery is not designed for discharge at that rate. It may well be that an alarm system has a rather different charging characteristic from your Lidl charger which possibly is not suitable in this application. Some research on the Lucas website may reveal more.

[JonE]

Hopefully this aux pump will last longer as its under 2A, Robert. It's quite small.

I double-checked a 6V and decided the Lidl unit must be faulty as it was now doing exactly the same thing.

Then realised I had forgotten to push the button once I connected the leads...oops.

4 months of kids off school is taking its toll.

[Bob Culver]

The continuous voltage to just maintain a fully charged battery is about 13.2 but many float somewhat higher. Many of the modern sytems supply an intermiitent or pulsed charge which is  confusing.With the advent of Ca batteries the whole topic of in and out of car charging has got complicated and the case against unregulated systems unfortunately increased.

[Renaud]

does any one run an auxiliary battery for other 12V items on your car?
I bought a low Ah Lucas alarm battery new from Tayna and have recently popped it on the LidL charger. It doesnt do what the car batteries do and ramp up the 4 bar levels in the display. It has just risen to 12.8V and no visible bars. No further rise in a 24 h period.
Just wondered if that sounds correct?

Despite all the right stuff that was said above I still don't like your battery not getting more than 12.8 V. It's a sealed lead after all. I don't know that Lidl charger but I would have tried another just to confirm?

[JonE]

all fine - went up to 14.4 and now 4 bars are showing, gradually lowering down a bit.
Just shows - always make sure you press the button.