2015 REx dead and not charging

[Nolan Montague]

Hello everyone, I have a 2015 REx that has been sitting in my garage for the past few months not on the charger. I have been checking on it every week or so and turning it on, but have not taken it out for a drive. Recently, I tried to turn it on and it showed a large amount of warning lights, and promptly turned off after that. It has not been able to turn on since then. I suspect that it is a problem with the 12v. Does anyone know if I can hook it up to a battery charger or jump starter? I do not want to buy a whole new battery and go through the process of installing it as well. Any help is greatly appreciated!

 

[EvanstonI3]

When the 12v battery is in good condition, the car's DC-DC converter converts High Voltage from the main battery to 14.8v DC to keep the 12v battery charged. The normal voltage of the 12v battery is about 12.9 volts when it is just resting.

If the 12v battery self-discharges over time, the DC-DC converter is supposed to come on, all by itself, and boost the 12v battery for One Hour. It should continue to do this.
However, if your 12v battery is failing, this will not help much and the car cannot keep up to keep the 12v battery charged. That seems to be what is happening here.

This does not work like an ICE vehicle where once you get the battery jumped or charged, everything is fine for awhile. It really sounds like the 12v is failed and jumping it or "charging" it will not help you. The 12v battery will no longer hold a charge that will allow it to operate the electronics of the car. The only solution I see is to replace the battery. Once you do that you will still have to either clear all the error codes and/or plug the car in for about 24hrs. The car will actually "repair" itself in a way if this is done.

 

[alohart]

I suspect that it is a problem with the 12v. Does anyone know if I can hook it up to a battery charger or jump starter?

As EvanstonI3 wrote, your 12 V battery should have been maintained automatically, so I, too, suspect that your 12 V battery has failed. This automatic 12 V battery maintenance feature isn't documented AFAIK, so it might not apply to all i3's. You could try to charge your 12 V battery with a 12 V battery charger. To do so, first disconnect the high-voltage disconnect to prevent potential damage to the DC-DC converter. Then connect your battery charger and cross your fingers that your battery will still hold a charge.

 

[Nolan Montague]

As EvanstonI3 wrote, your 12 V battery should have been maintained automatically, so I, too, suspect that your 12 V battery has failed. This automatic 12 V battery maintenance feature isn't documented AFAIK, so it might not apply to all i3's. You could try to charge your 12 V battery with a 12 V battery charger. To do so, first disconnect the high-voltage disconnect to prevent potential damage to the DC-DC converter. Then connect your battery charger and cross your fingers that your battery will still hold a charge.

Thank you for your help. Could it possibly be that the cars battery was dead/too low to recharge the 12v and in turn the 12v died? Could that mean that the 12v is still good and maybe just needs to be recharged? Maybe I should try to take the battery and and charge it at auto zone? Thank you again for the help

 

[alohart]

Could it possibly be that the cars battery was dead/too low to recharge the 12v and in turn the 12v died?

Because automatic 12 V battery charging isn't documented, I don't know whether there's a charge level limit below which automatic battery charging won't occur. Because the usable capacity of even a 60 Ah battery pack is 78 times that of the 12 V battery, charging the 12 V battery doesn't decrease the charge level of the battery pack noticeably unless the 12 V battery won't hold a charge and is automatically charged multiple times.

Could that mean that the 12v is still good and maybe just needs to be recharged?

I have charged the 12 V battery in our i3's with a standard 12 V battery charger when the battery's voltage was lower than expected. During the pandemic, I didn't drive our i3 enough to keep its 12 V battery charged, so charging it with a battery charger increased its charge level sufficiently. Eventually, the 12 V battery failed and wouldn't hold a charge for very long, so charging it with a battery charger didn't help.

Maybe I should try to take the battery and and charge it at auto zone?

The 12 V battery can be charged without removing it. However, if you don't have a battery charger, removing the battery and taking it to Autozone would be an alternative worth trying. Battery chargers can detect certain battery failure modes.