Aux Battery Clarification

[Frank_Butcher]

Hi All - newbie here and looking for advice on aux battery charging behaviour. Have found a few threads but not seen conclusive answers there.

- At idle, i.e. no start, no hookup, I see a voltage of c.12V +/- , often (but not always) with the 'unable to determine charge' indicator on the central controller.
- On hook up, I see verrrry slow charging (with the charging indicator reported on the central controller) - incrementing a few tenths in say a 12 hour period.
- When driving, I see 14.4V, with the charging indicator displaying fully charged on the central controller. When turned off the display drops back to the c.12V range again.

There are no consumers on, e.g. fridge.

Two questions if I may. Is this flaky behaviour 'normal'? And what is the true charge of the aux battery in this scenario?

Note that the battery was left to go down to the 8V range when on the forecourt so there could well be degradation - another reason for asking before I go back to them.

Thanks in advance for any guidance.

 

[James G]

that's the same behaviour as my auxillary battery for the last 3 years. I've also let me aux battery go flat over lockdown but it seemed to resurrect itself just fine despite the warnings in the manual

 

[Frank_Butcher]

Thanks James - much appreciated.

 

[Samebutdifferent]

If you discharge the battery below 50% SOC it can cause damage and shorten it's life.

10.5v is 0% SOC a dead battery that may well never recover.

All voltages are at rest, no load for 1hr.

 

[Frank_Butcher]

Thanks SBD. My aux battery is not holding charge either (down to 10V range in 3 days with no draw), so it's time to activate that warranty methinks.

 

[Samebutdifferent]

Thanks SBD. My aux battery is not holding charge either (down to 10V range in 3 days with no draw), so it's time to activate that warranty methinks.

Definitely a dead battery. Think also about the starter battery, if they didn't put on hookup then that may well have suffered the same fate.

 

[Frank_Butcher]

Definitely a dead battery. Think also about the starter battery, if they didn't put on hookup then that may well have suffered the same fate.

Yup - thanks, will have them check. Interestingly, the sales guy asked the service dept to charge the aux. battery but they didn't even have hook up cables in the shed. He himself went to a DIY store to get a set and at least got some charge into it so he could demo features. I guess this may well be the case with many approved used MPs that are sat around for a while.