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Discussion Starter · #1 ·
Can anyone think of a good reason why I could not substitute a AGM 12V battery of Group 35/85 for its oem Group 47 one? The sizes seem to be near identical as well as ratings. I am going into the 9th year of my 2014 12V original battery though the car is garaged without issues so far per the battery test checks. But I might preempt it with the caviate the Group 47s are getting harder to come by and if there is just a slight differences in size of Group 35/85 being smaller here am there by less than a 1/4 inch or so and as I said near identical othewise.
 

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Can anyone think of a good reason why I could not substitute a AGM 12V battery of Group 35/85 for its oem Group 47 one? The sizes seem to be near identical as well as ratings. I am going into the 9th year of my 2014 12V original battery though the car is garaged without issues so far per the battery test checks. But I might preempt it with the caviate the Group 47s are getting harder to come by and if there is just a slight differences in size of Group 35/85 being smaller here am there by less than a 1/4 inch or so and as I said near identical othewise.
You need the Group 47 battery. There is a tray of fuse Links on + side of the battery designed to fit exactly with the battery case. I’m not saying, you can’t use the other. If it weren’t for that tray, It probably wouldn’t matter. Stick with direct fit replacement, no worries that way. I just had to replace my failed 9 year old battery just before thanksgiving.
 

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Discussion Starter · #3 ·
You need the Group 47 battery. There is a tray of fuse Links on + side of the battery designed to fit exactly with the battery case. I’m not saying, you can’t use the other. If it weren’t for that tray, It probably wouldn’t matter. Stick with direct fit replacement, no worries that way.
Good to know. I was preplanning if the G47 is not available and I had no real choice and the 35/85 is nearly identical in shape/size and not bigger for sure than the original so the mention you make should still fit back. Thanks.
 

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Good to know. I was preplanning if the G47 is not available and I had no real choice and the 35/85 is nearly identical in shape/size and not bigger for sure than the original so the mention you make should still fit back. Thanks.
When mine failed, I feared it would be some special order battery. As luck would have it, the O’reilly autoparts store I went to, had one in stock. Since, you are pre-planning, you might as well just get one now while you can shop for the best deal on a G47. That way it’s on your terms and convenience. Mine failed, on a trip. I was lucky I only lost a day of work over it. I was so happy they had the exact fit battery in stock, I didn’t think twice at the $197.00 price. Then the counter guy said, it was an AGM. Then I understood the high price.
 

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Discussion Starter · #6 ·
I changed my 12V in my 2011 about a year ago. Walked into a NAPA store, no problem, they had the 47 AGM on the shelf.
Good to hear you got 10years as it seems out of your battery...maybe I will get that too now going into my 9th year as a garaged car as opposed to sitting in the cold all the time in the NE winters or hot suns in summer.
 

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The 12v AGM battery has an easy life in our Volts. Its main purpose is to fire up computers, not crank a cold ICE. Good to carry a small lithium battery booster pack to boot the computers up if or when your OE 12v can't. There is a caveat about accessing the trunk with no power, but the terminals under the hood are there for boosting. See your owner's manual. I'm 10 years in on the OE AC Delco unit.
 

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Discussion Starter · #8 ·
The 12v AGM battery has an easy life in our Volts. Its main purpose is to fire up computers, not crank a cold ICE. Good to carry a small lithium battery booster pack to boot the computers up if or when your OE 12v can't. There is a caveat about accessing the trunk with no power, but the terminals under the hood are there for boosting. See your owner's manual. I'm 10 years in on the OE AC Delco unit.
Yes I know but if it suddenly holds no charge and I am 700 miles from home that might not keep the engine running or does that stop/start totally rely on the traction battery...I forget and not the 12v? But yes I just bought a lithium battery pack. And yes the posts under the hood would assist in attaching the battery pack once key opens the doors. But if the 12v is needed to start/stop engine once its booted up then I suppose a strapped lithium pack might do the trick too under the hood at worst case. I hope it is the traction battery that is the start and stop of the engine since on long travels I tend to now drive in HOLD mode not using up the traction battery charge until I am near home again just for t hose mountainous I84 or I80 or etc. hills....(-;
 

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Yes I know but if it suddenly holds no charge and I am 700 miles from home that might not keep the engine running or does that stop/start totally rely on the traction battery...I forget and not the 12v?
Yup. Starting the engine uses the main battery. You have a 70+ HP starter motor. The engine will turn over when starting, no question about that. Some people find it hard to tell when it actually starts burning fuel because the starting happens at 1400 RPM or something. The 12v gets the computers going, and connects the main battery, which then feeds the aux power module and that takes over for the 12v. So the aux battery never has to supply much in the way of amps, but it does need to maintain voltage while those amps are being drawn. (and this is where we have to dive into metaphor and start talking about internal resistance and stuff to go deeper, but it's usually enough to just remember "It's different. Normal 12v testers can be wrong.")
 

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Yup. Starting the engine uses the main battery. You have a 70+ HP starter motor. The engine will turn over when starting, no question about that. Some people find it hard to tell when it actually starts burning fuel because the starting happens at 1400 RPM or something. The 12v gets the computers going, and connects the main battery, which then feeds the aux power module and that takes over for the 12v. So the aux battery never has to supply much in the way of amps, but it does need to maintain voltage while those amps are being drawn. (and this is where we have to dive into metaphor and start talking about internal resistance and stuff to go deeper, but it's usually enough to just remember "It's different. Normal 12v testers can be wrong.")
My real life experience of a Failed 12V was “engine not available “ on my way work one cold morning without enough HVPack capacity to turn around and get back home. I was lucky to find a location within range to at least plug in to 120V to slow charge for 6 hours figuring I would just drive home to deal with the issue. Well, when I tried to power up after the Pack was topped off, the car was very slow to go through start up initialization. Then it started doing very wonky things like flipping back and forth between Battery only and ICE startup. I had heard about weird things happening if the battery was going bad. I removed the 12V and took the to a local O’Reillys nearby. It tested 12.19V “bad”. The startup loads were probably just enough to pull the Voltage down below some of the electronic minimum voltage thresholds. Fortunately, they had a G47 in stock. Tested 12.6V (100% SoC). 20 minutes later I had a fully functional Volt again
 

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Type 47 is small but not especially rare (my 1980 TR7 uses it). 47 AGM's might be rarer. Local Canadian Tire didn't carry it in stock, nor did the next town up (36 miles) but the next up up did (another 15 miles). There were several Canadian Tire shops in city down from me (35 miles). I happened to get a good deal ($200 on sale with a $50 gift certificate on sales $200 or higher, it was Xmas time). Effectively $150 (or $97.50 in American money, $120 now, exchange rates different now). It was an exact match to the original ACDelco. I returned the old battery for the core refund at local CT to get stated prices. Sometimes timing is everything.
 

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You need the Group 47 battery. There is a tray of fuse Links on + side of the battery designed to fit exactly with the battery case. I’m not saying, you can’t use the other. If it weren’t for that tray, It probably wouldn’t matter. Stick with direct fit replacement, no worries that way. I just had to replace my failed 9 year old battery just before thanksgiving.
if the battery is the same width,there will be no problem.I just put 2 bigger batteries in my truck,length was 1.5" longer.the 2 boxes that sit on the battery still fit,granted I had to shoehorn the batteries in.I went from group 48 agm to 94R agm(more power available) and the 94's were cheaper,$180 vs $160.
look at the specs,pull out the tape measure and see what you can fit.I did
 

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Discussion Starter · #13 · (Edited)
BTW I Iet my volt sit charging since Saturday night plugged in at home as simply did not drive it cause I have to exercise my Tacoma now and then which is a 2008 with only 26k miles. Today 2.5 days later on the Volt I decided to check the 12v battery condition. My meter said good state but charge and had 12.24v reading. So I drove it today mostly with engine running because of the 15F override run some 24mile round trip and tested it again. It said good with NO charge needed and was showing 12.63v. My question is at what point and 12voltage drop do folks experience problems nutty electronic experiences? Some say below 12.2v or?
 

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Discussion Starter · #14 ·
if the battery is the same width,there will be no problem.I just put 2 bigger batteries in my truck,length was 1.5" longer.the 2 boxes that sit on the battery still fit,granted I had to shoehorn the batteries in.I went from group 48 agm to 94R agm(more power available) and the 94's were cheaper,$180 vs $160.
look at the specs,pull out the tape measure and see what you can fit.I did
And that is exactly what I am doing. The size is less than 1/4 inch in width and length and the height is slightly lower too. The only shape difference seems be the OEM has recessed like sidwalls around the posts while the alternate is just posts up on top of the battery but again the overall height is slightly lower. And your right pricing is also the difference.
 

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BTW I Iet my volt sit charging since Saturday night plugged in at home as simply did not drive it cause I have to exercise my Tacoma now and then which is a 2008 with only 26k miles. Today 2.5 days later on the Volt I decided to check the 12v battery condition. My meter said good state but charge and had 12.24v reading. So I drove it today mostly with engine running because of the 15F override run some 24mile round trip and tested it again. It said good with NO charge needed and was showing 12.63v. My question is at what point and 12voltage drop do folks experience problems nutty electronic experiences? Some say below 12.2v or?
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Discussion Starter · #16 ·
Also is our AGM oem battery Gel based? The tester selection for AGM was Gel, Spiral and one other.
 

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:p
AGM is glass mat, I think that's different from GEL which I think Optima is (it's also spiral so would have the same setting). I measure battery and fit for my '88 Toyota Tercel 4X4 wagon which I routinely have difficulty match aftermarket parts to as I think the charts tend to throw it in with the Tercel sedan, totally different car.

I had lost my compass for a couple months. I happened to read battery when I had the back open and it was 11.9V. Changed it, compass came back. No idea what it read at the time the compass went, still new to the car and it wasn't a big deal. Not hard to know the direction you are going, Ocean to the East, mountains to the West, sun to the South, no sun to the North. Hard to get lost.:p
It was original battery, 6 years old.

When you drive it, the main battery will charge it. It will hold that charge for a while. You can not use your car for a month without it affecting anything if the 12V battery is good. I'd keep an eye on it checking it every so often if it is left foe a while (day or two) to get a handle on it over time. I carry a Lith. battery booster under front seat in case I ever need to boost it in the future plus if a friend's ICE ever needs a boost you can help out with out using the "correct" way to do it from the Volt.
 

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Discussion Starter · #18 ·

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I tested it today 1 day later and it sat at 12.46v and 92% good or so and 64% charged or so per meter suggestion.
After a day? I'd consider that battery a candidate for replacement. The "rested" voltage (several hours after being charged so the slight overchage or "surface charge" gets integrated) should be around 12.7-12.8 for a healthy AGM battery and might be 12.9 for a new one. Gel would be higher yet by a tenth or two, but Volts don't use those.
 

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Discussion Starter · #20 ·
After a day? I'd consider that battery a candidate for replacement. The "rested" voltage (several hours after being charged so the slight overchage or "surface charge" gets integrated) should be around 12.7-12.8 for a healthy AGM battery and might be 12.9 for a new one. Gel would be higher yet by a tenth or two, but Volts don't use those.
Yeah thats what I am planning while still doing local trips but I have a lithium battery pack just in case before I replace it. My dealer had part pricing of oem a year ago of $159 for the battery and then I think $30 to install it. I will have to recheck this coming year/spring/summer.
Thanks all.
 
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