Replacing the 12V aux Battery

[X.l.r.8]

Because it’s smaller I personally would bulk it out with the rigid insulation foam keeping the temperature constant. If the temp drops I suspect the pack will charge it warming it back up again. I know I’ll be throwing it in mine when this one starts playing up, but so far I haven’t had to walk that path.

 

[n2mb_racing]

Shorai have a bms, as do Lithiumax, the other one referenced also had one but that was north of $500. As for the rest, I doubt it. My friend went to lithium in his motorcycle because he was tired replacing it every year. He researched and ended up with the same Shorai battery. Mostly because it was one of the few that had a BMS.

I don't think Shorai has an integrated BMS. They have a BMS port and an external balance charger that you can plug in. So, as long as you periodically do a balance charge using their balance charger, that would be ok. But, I don't know how often you'd have to do it, since the Roadster probably charges and discharges the battery more often than most cars would.

 

[X.l.r.8]

He has never had to use the charger. I did ask him that. The Lithiumax May be the way to go. However I have an idea if I buy a BMS I have enough cells to quickly build a 12v battery. I don’t have any boards that small right now but I will look into it. I thought my battery building days were over.

 

[Stefan T]

The shorai battery worked well for me
It work without problems in little more than 3 years in my first roadster to the house burned down that the roadster were in

 

[hcsharp]

I'm still a little bit unclear on the lithium car batteries.... Do they have a balancing circuit or not? They seem to be 4S batteries that are constantly bulk charged / discharged. Once in a while the cells should be balanced. Unclear how the drop in replacements do that.

I might also be slightly concerned about a drop-in lithium ion battery, since the car will attempt to charge it at any temperature. Lithium ion batteries usually can't be charged below freezing without damage.

It seems like it could be done correctly, but I'm not sure if any of the drop-in replacements do all the right battery management things.

I have the same concerns. Unless it has a heater then it's useless in my climate. I certainly won't buy one because of all the disadvantages and few if any advantages.

• Needs a heater. Insulation alone won't work. The heater will use extra energy. Not worth it.
• Needs battery management for charging and balancing. Need to investigate whether this is performed automatically. If not, it's too much of an inconvenience.
• Much more expensive than a regular AGM battery with almost no upside. OK, theoretically you won't have to replace it as often, so maybe price is comparable.
  
• Capacity is less than comparable AGM battery. If it is using 4S packs then the nominal voltage is 14.8 and peak of about 16v which is too high so you won't ever get the full capacity. I don't know if it has a BMS with a step-up voltage device and regulator that takes care of this but the OEM battery only charges to 13.6v.

Just my .02

 

[gregd]

+1 to Henry. Like it or not, an AGM / SLA battery is really ideally suited for this application, especially if the car will be subjected to really cold temperatures.

As to cycling of the battery, it might be worth taking a voltmeter to yours. When I had mine replaced some 3 years ago (due to the same message), I had the Service Center wire in a power pole connector in parallel with the battery, up into the under-hood area (where I could get to it). The idea was that I could use it to "jump" the car if necessary, since the physical battery is so inaccessible, but the connector has been an interesting portal into the state of the battery's charge. To the surprise of the SC techs, mine seems to stay within 0.01v of a constant 13.77v, regardless of the car being awake, asleep, or charging. No cycling that I can detect. No fault in the car, that they can detect. {shrug} My car is a 2.0.

So, a battery or system that requires a spike to over 14v for charging and other BMS functions (relying on the behavior of a classic alternator) is just not going to be happy in my car. It may work, but likely not in an optimal fashion. And every lithium battery available to the consumer has a small battery regulator circuit built in, for safety. This prevents charging if the battery is ever fully discharged (below the anti-bricking level), for example. Remember how your laptop battery just "died" one day, refusing to accept any charge? That's the reason. One of the cells got unbalanced, and during a discharge went "below zero", triggering the shutdown. The circuit should also prevent overcharging, as both over-charging and charging from zero are very dangerous and will lead to a fire. So, there are levels of BMS for Li-ion batteries, but all but the raw cells do have some BMS function built in. The rest may be marketing fodder.

 

[smorgasbord]

• Much more expensive than a regular AGM battery with almost no upside. OK, theoretically you won't have to replace it as often, so maybe price is comparable.

Yeah, that was my reasoning - it's not super easy to get to, so I was looking for something to last longer then the 3.5ish years I've gotten out of my two batteries thus far. I live in NorCal, so it's almost never freezing, btw.

In another 12volt thread here, someone recommended this battery: Tesla Roadster 12V Secondary Battery | eBay

Any thoughts? 12AmpHours instead of 8 can't be a bad thing...


True Story: When the car was under the original warranty, I had some work done by Tesla on it. I picked the car up the next day and drove away. Went to a restaurant for lunch. After lunch, the car wouldn't unlock. I finally tried opening the charge port door, and then was able to unlock the car. Drove straight back to Tesla.

Turns out they had forgotten to reconnect the battery!

 

[hcsharp]

Any thoughts? 12AmpHours instead of 8 can't be a bad thing...

I spoke with a service tech (so you have to take it with a grain of salt) who said anything more than 8ah is not good for the car. The reason he gave was that it would draw too much current while charging which would create undo stress on the charging system for the 12v battery. Regardless, I plan to use that Gruber 12ah battery the next time I replace mine. I've heard anecdotal reports that it's a reasonably good quality battery and it's being used in a lot of Roadsters. I've also used their batteries in my UPSs with good success.

 

[n2mb_racing]

I spoke with a service tech (so you have to take it with a grain of salt) who said anything more than 8ah is not good for the car. The reason he gave was that it would draw too much current while charging which would create undo stress on the charging system for the 12v battery. Regardless, I plan to use that Gruber 12ah battery the next time I replace mine. I've heard anecdotal reports that it's a reasonably good quality battery and it's being used in a lot of Roadsters.

Seems unlikely. The charger in the car sets the charging current, not the battery. It will cycle less frequently, since it has larger capacity. That should make it last longer. However, it is probably heavier than the stock battery by a small amount.

 

[ShawnA]

Hi Smorgasboard,

I am the one that installed the Gruber/eBay 12 volt 12 amp/hour battery.
It is smaller than the original battery.
I only installed it a year ago, so I cannot give a battery lifetime reference.
It still works well for me.

The battery I removed was an Interstate FAYTX9.
This was the battery Tesla installed after the previous failure.
One of the cells appears to be bulging...

In the small print for the lithium battery referenced on Amazon it says:
"Needs no maintenance for 1 year."
The standard battery requires less maintenance than that.

Shawn

 

[smorgasbord]

On the lithiums, I found this on Amazon. It's less than 1/3 the weight (2lbs) of the standard battery (almost 7lbs), but there are a bunch of caveats printed right on the battery. Here's a couple concerning items:
1) Charging voltage must be between 14 and 15 volts. Less than 14 volts and you don't get a full charge, more than 15 volts damages the battery.
2) The Wh rating is 60, so it's only 5 amp-hours. That's less than the 8Ah of the OEM battery.
I don't know enough to have confidence in these lithium replacements.

BTW, the "Needs no maintenance for 1 year" refers to the battery's ability to hold a charge. For stand-by applications, you can charge the battery and let it sit for up to one year before its internal self-discharging has drained it completely.


I found this battery that supposedly meets OEM specs for $30, free shipping. It weighs 6.72 lbs. There's a also this 9Ah gel version, which weighs 8.37lbs and costs $10 more. Looks like weight is proportional to Amp-hour capacity. Searching on Amazon for "YTX9-BS" brings up a big list of alternatives, but there really seem to be only these variants:
1) 8Ah with acid you fill.
2) 8Ah ships complete.
3) 9Ah ships complete.
4) Lithium batteries.

The YUASA YTX9-BS battery specs are here: YTX9-BS - Yuasa Battery, Inc. (6.6 lbs, 8Ah, made is US). Ships dry with acid separate. Yick.

The Interstate equivalent weighs 7.51 lbs at 8Ah: Interstate Batteries | FAYTX9 , and costs 3X the price. It ships complete with no acid handling required. Interstate batteries have a good reputation - I don't know if that's still deserved or not. Since it's heavier, it might be under-rated (a good thing).

I'm probably going to order the Gruber later today. Seems worth the extra money to potentially not have to replace it as often (12Ahours). I think that a high amp-hour rating should not affect anything in terms of the car charging system.

 

[X.l.r.8]

The problem is that most applications can handle the additional voltage of a 4S pack, but if you drop to a 3S pack with additional amperage, not only can you use cheaper cells, but at a nominal 3.7v per cell or 11.1v pack voltage and conservative 4.1v max or 12.3v pack would work well depending on the charge output from the main pack. I’ll have to look through the manual to see what that is but even fed through a lithium charger. $5 circuit board that tapers at 90% of full charge and totally adjustable. It’s totally reasonable to have a pack with more Amps. I use my packs through winter totally exposed to the elements and I lose amperage not voltage. I deliberately built in twice the needed range to compensate for winter. That being said if I go full power when it’s really cold once the pack warms up
I recover range. In a storage application with constant charge ability I doubt it will be a concern.

 

[smorgasbord]

So, it turns out my company uses Yausa batteries in its products, and the YTX9-BS is available to me at a substantial discount. So, I'm going with that.
I'll come back to this thread when it dies.

 

[smorgasbord]

Finally got around to doing the replacement. Easier to do than I thought. FWIW, the old battery measured 12.75 volts a few hours after being uninstalled. But, apparently, that's not high enough to ensure reliable operation of doors and trunk, as I had many first-time failures before and none in the few times I've tried since replacing the battery.

 

[Story]

This is a really helpful thread, folks, thanks from the future....the last post was 7.5 years ago!

Dave

 

[jfischer]

I replaced my dead Tesla 12V batttery with a AGM FAYTX9 type without any issues. Exact same size, bolts, etc...

Went by this guide with pictures and worked exactly as explained .

I did have a lift so I could work at eye height which helped. The bolts on the bottom side are a bugger to get to unless the car is lifted up a decent height. I only WISH Tesla would have used galvanized or rust proof bolts, screws on the wheel well and below. ... seems they will rust out or seize more easily. I guess my next replacement will include retrofitting those bolts as well.

 

[Mark77a]

ACE workshop (aka Hanger )

 

[Story]

OK, longtime lurker, first time poster...

I noticed in the thread that several people had their car work without a 12V, and about 4 years ago(!) Spaceballs just happened to mention in the thread "I've got my car modded so it doesn't have a 12V."

Since I've had my 12V replaced once already 3-4 years ago, and it's low voltage again, I'm wondering if I can simply eliminate the need for a 12V battery at all.

Has anyone got a pointer to Spaceballs' mods or ideas on how to eliminate the need for the 12V altogether?

 

[spaceballs]

... Has anyone got a pointer to Spaceballs' mods or ideas on how to eliminate the need for the 12V altogether?

On the 2.0, I just disconnected the 12v battery and left it disconnected and I never got an error message. So i left it that way until Tesla did the R80 upgrade and put in a new 12v.

 

[gregd]

On the 2.0, I just disconnected the 12v battery and left it disconnected and I never got an error message. So i left it that way until Tesla did the R80 upgrade and put in a new 12v.

{TILT} What is the battery for, then?

It's been said that the way to make a TV set cheaper is to start clipping out parts until it stops working, then put the last one back in. Did Tesla miss an opportunity here?

Also, how does the car determine that the battery is "low", if not having it present (the ultimate "low") doesn't count? Is it more a matter of the battery drawing excessive charging current that sets off the error?