12V battery

blackscraper · Sep 22, 2016

Is the 12V battery be hooked to charger when the car is parked? Especially when the car is connected to the shore power. This way, it can greatly enhance the lifetime of the 12V battery. If the answer is no, then why?

I kinda remember this question was raised somewhere. But I can't find it right now.

JPP · Sep 22, 2016

The 12V is monitored by the on-board electronics. If the voltage drops, then it is charged from the main traction pack through the DC-to-DC converter, whether or not the car is connected to external power or not. Nothing to worry about.....

blackscraper · Sep 22, 2016

I'd be worried about that if the battery keeps cycling while sitting idle. A replacement happening every 2 years is widely expected. After warranty, it will cost several hundred dollars. This counters the claim that EVs cost less to maintain. I don't see any reasons why the the battery can not be isolated and/or standing by while the car is plugged in.

JPP · Sep 22, 2016

I'm sorry--you want the 12 battery to be disconnected from everything to preserve its charge? Not possible, and not possible with modern ICE vehicles. There is always some 'vampire load' from on board electronics (alarm systems, LTE modem) which will deplete the battery eventually. In an ICE car, if you let it sit too long, the battery discharges and the car won't start. If the 12V in a Tesla is depleted, the car won't start either. Difference is that in a Tesla you have the massive traction pack to top off the 12V. FWIW, very few Tesla owners are seeing replacement every 2 years. There were some early issues with bad 12 batteries. Maybe you want to take a few minutes and search these forums for way too much good information on this issue.

Tripple_T · Sep 26, 2016

I'll place this here. Might help understand the replacement challenges.

nwdiver · Nov 3, 2016

I just spoke to Tesla about getting my 12v battery replaced. They're emailing me the quote but I was informed over the phone that the cost of the battery has been increased from $125 to $400. If it's still a crappy AGM I'm not going to be happy... For $400 it had better be a lithium Ion that will last at least as long as the main pack.....

wesley888 · Nov 3, 2016

Unfortunately, afaik, it has to be a lead-acid battery due to the wide range of operating temperature. Without the 12V, nothing else can even start their operations.

Tripple_T · Nov 3, 2016

$125 is for the battery by itself (IE: you replace it). $400 sounds like the price they would charge to replace the battery and a bunch of stuff that doesn't need to be replaced.

Pando · Nov 3, 2016

Why have that battery there in the first place? Couldn't the DC-DC converter be used to power whatever needs to be powered from the main pack?

brkaus · Nov 3, 2016

Pando said:
Why have that battery there in the first place? Couldn't the DC-DC converter be used to power whatever needs to be powered from the main pack?

covered many times.

- the 12v can keep safety systems operational for a brief time if the DC-DC fails. So one can safely stop.

- the 12v power is used to keep the main pack contractors closed. Gives emergency responders a way to ensure the main pack is isolated. They cut the "safe" 12v loop ad the HV is disconnected.

nwdiver · Nov 3, 2016

brkaus said:
covered many times.

- the 12v can keep safety systems operational for a brief time if the DC-DC fails. So one can safely stop.

- the 12v power is used to keep the main pack contractors closed. Gives emergency responders a way to ensure the main pack is isolated. They cut the "safe" 12v loop ad the HV is disconnected.

Its use is FAR worse than that... the battery is typically cycled ~5x per day. The car beats the living crap out of that poor little battery. This is an obvious design flaw. It's frustrating that Tesla is forcing its owners pay for such a glaring oversight.

I asked specifically if the $400 was including labour. I was told no. That's just for the part.... unless I was misinformed. You can use other chemistries for the 12v battery. This is a 3rd party option for a lithium ion battery...

brkaus · Nov 3, 2016

I agree the impact/usage is far worse. But those are the ease one for a separate 12v system.

nwdiver · Nov 3, 2016

brkaus said:
I agree the impact/usage is far worse. But those are the ease one for a separate 12v system.

Having a separate 12v system isn't the problem... the battery should be kept on a float instead of being cycled.

brkaus · Nov 3, 2016

nwdiver said:
Having a separate 12v system isn't the problem... the battery should be kept on a float instead of being cycled.

Yes, my understanding is the large DC-DC and contactors have a reasonable power draw themselves. Hence the cycling. Perhaps they need a smaller DC-DC and contractors to float the 12v battery at all times.

GJ79 · Nov 4, 2016

Has anyone tried their drop in replacement yet ?
BattMobile Batteries, Custom Lithium Batteries

nwdiver · Nov 4, 2016

GJ79 said:
Has anyone tried their drop in replacement yet ?
BattMobile Batteries, Custom Lithium Batteries

No... I'd like to but it's not available until December and I'm not sure my 12v will last that long...

I also heard back from Tesla. The battery is $144... so I'm pretty sure it's still the same POS AGM

brkaus · Nov 4, 2016

Of course, there is complexity at the HV junction box or chargers, but if they could tap off the charger circuit and float charge the 12v when it's plugged into AC... a plugged in Tesla would be an even happier Tesla.

Might even save electricity overall.

nwdiver · Nov 4, 2016

brkaus said:
Of course, there is complexity at the HV junction box or chargers, but if they could tap off the charger circuit and float charge the 12v when it's plugged into AC... a plugged in Tesla would be an even happier Tesla.

Might even save electricity overall.

Yeah... trying to think of an easy way I can keep my battery connected to a Battery Tender... but I shouldn't have to plug my car in twice

GJ79 · Nov 4, 2016

nwdiver said:
No... I'd like to but it's not available until December and I'm not sure my 12v will last that long...

I also heard back from Tesla. The battery is $144... so I'm pretty sure it's still the same POS AGM

I guess for $144 I would go with teslas battery. You can buy almost 3 of them for the price the Battmobile one would cost you.

brkaus · Nov 4, 2016

nwdiver said:
Yeah... trying to think of an easy way I can keep my battery connected to a Battery Tender... but I shouldn't have to plug my car in twice

I'd be the first to drive off with it plugged in. Ripping the cord sideways from the outlet and with my luck scratching the car.

12V battery

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