Bit of a 12v AGM dilemma

[Shawty]

So I bought a 2015 gx4h from salvage. I've been working on the car for the last couple of weeks figured I would check the aux battery , pulled up the boot floor to measure the battery and it was at 11.5, everything still working ok....

The car has WiFi, but not connected as no card with the car so it's not been doing it's 2pm WiFi charge for the last 6 weeks, I have been running the car intermittently which I guess has put some charge on but , activating the auto boot etc has probably worn the battery down.

Reading up about AGM batteries is a bit of a minefield.

Questions I had can I trickle charge from the boot direct to the aux battery? ( I've been doing this the last day or so) Or do I need to do it via the engine fuse box or is either fine?

Currently the battery is settling down around 12.35 which seems low to me but AGM sites suggesting 12.3 is 70% charge and ok.

Do I just need a new battery?

 

[AndyInOz]

The user manual for my 2014 only offers the engine fuse box method for externally charging the auxiliary battery.

(Terminal post with a flip up cover in the fuse box, and a metal bracket on the cooling system overflow bottle (I think that's what it is) for for ground).

12.3 sounds fine for the battery.

Bear in mind, it will not be recharged by the car, unless there is power in the drive battery.
(We usually call it the 'traction' battery, but I see that Mitsubishi use the terms 'drive battery' and 'auxiliary battery. In my manual, at least.)

 

[Hhl1]

The connection under the bonnet seems to connect to the battery through a diode, so if you use a smart charger it may not work. Best to connect direct to the battery then.

 

[michael8554]

Check when the car is ON that the battery volts rise to about 14V, showing that the car is charging the battery.

 

[Shawty]

The car charges the battery fine up to about 14.6 it seems. This is the last few days on an ancell Bluetooth battery monitor. The left spike on AGM charger, the right spike with the motor running today . Intrigued at to what the 3 hourly energy usage is, every 3 hours , is it the WiFi searching perhaps

 

[Polyian]

The connection under the bonnet seems to connect to the battery through a diode, so if you use a smart charger it may not work. Best to connect direct to the battery then.

I don't understand the issue. All a diode does is allow current to flow in one direction only. This would prevent reverse hookups from damaging electronics. I fail to see how a diode would would prevent a charger from working if connected properly. Maybe I'm missing something?

 

[PHEV07]

Check when the car is ON that the battery volts rise to about 14V, showing that the car is charging the battery

I don't understand the issue. All a diode does is allow current to flow in one direction only. This would prevent reverse hookups from damaging electronics. I fail to see how a diode would would prevent a charger from working if connected properly. Maybe I'm missing something?

You are correct. Diode on Red Post Fuse Box will allow current to flow into PHEV Battery but not out of the PHEV to charge another Vehicle Battery.

Quite ingenious.

Just wish they used the sane smarts to have installed a Battery Heater on the Drive Battery Pack of the 2023 to 2025 PHEVs

Another topic I know...... but....

 

[Hhl1]

Most small automatic chargers will not start if they don’t see 12V, and even if they do, the extra voltage drop will confuse the sensing,,