Trying to add 2nd battery in the trunk 2015 passat tdi

MAXRPM

Veteran Member
Joined
May 7, 2008
Location
US
TDI
00 Jetta and 99.5 Golf, 2015 Passat TDI,BMW 2
I bought a lead battery from Costco about 8 months ago for my passat, i'm trying to add a 2nd AGM battery or anything that is sealed, for the trunk, would I be able to mix a sealed and lead battery to work in conjunction hopefully they wont get ruined, does anybody know what kind of cranking amp the costco battery got, so if I'd able to hook them up I could get same cranking amps on both, and any advice would be appriciated.
 

Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
COLORADO (SE of Denver)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress) I moved so now i got nothing but an AHU in a garage on a pallet.
Volts is volts. It will be fine. Just wire it up properly and locally ground it as well as to the other battery. Make sure your not going to overload the alternator.
 

ZippyNH

Veteran Member
Joined
Apr 22, 2015
Location
Southern NH
TDI
2015 JETTA TDI SE
Volts is volts. It will be fine. Just wire it up properly and locally ground it as well as to the other battery. Make sure your not going to overload the alternator.
Unfortunately they charge at different voltage best.....
I wouldn't do it... mixing battery types.
Return it, get two good ones of the same type.
 

scooperhsd

Top Post Dawg
Joined
Aug 19, 2003
Location
Kansas City KS
TDI
NB, 2000, RED(5 Speed conversion) 2015 Golf SE
Really, a 2nd battery is not necessary. Just have a good one in the engine compartment.
 

Lightflyer1

Top Post Dawg
Joined
Sep 13, 2005
Location
Round Rock, Texas
TDI
2015 Beetle tdi dsg
Yes lead acid batteries and AGM have different charging requirements. You should not mix the two, get two of the same and then wire them properly. But there is really no need for this at all. Just creating a new failure mode possibility and unnecessary expense.
 

Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
COLORADO (SE of Denver)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress) I moved so now i got nothing but an AHU in a garage on a pallet.
Yes lead acid batteries and AGM have different charging requirements. You should not mix the two, get two of the same and then wire them properly. But there is really no need for this at all. Just creating a new failure mode possibility and unnecessary expense.
Unfortunately they charge at different voltage best.....
I wouldn't do it... mixing battery types.
Return it, get two good ones of the same type.

yes but it does not matter on a car. a marine use or something YES

AGM's are about 5 years or 500 cycles. you will far exceed 500 cycles at 50% use each cycle of whatever use its for in a car. life wont matter to the point that its important to charge properly.

also AGM's are lead acid, its just suspended in a gell glass mat. nothing new here. slower charge is better. 7.5 amps is about right

it all comes down to what OP is using it for.
 

Lightflyer1

Top Post Dawg
Joined
Sep 13, 2005
Location
Round Rock, Texas
TDI
2015 Beetle tdi dsg
Read this:

"As with all gelled and sealed units, AGM batteries are sensitive to overcharging. A charge to 2.40V/cell (and higher) is fine; however, the float charge should be reduced to between 2.25 and 2.30V/cell (summer temperatures may require lower voltages). Automotive charging systems for flooded lead acid often have a fixed float voltage setting of 14.40V (2.40V/cell); a direct replacement with a sealed unit could overcharge the battery on a long drive. (See BU-403: Charging Lead Acid.)"

https://batteryuniversity.com/learn/article/absorbent_glass_mat_agm

The alternator or charger needs a special setting for AGM vs regular lead acid batteries. Using a regular charger for AGM will ruin it.

Seems to me the OP stated he wanted to connect the two for starting batteries and no other use.
 
Last edited:

MAXRPM

Veteran Member
Joined
May 7, 2008
Location
US
TDI
00 Jetta and 99.5 Golf, 2015 Passat TDI,BMW 2
I need it for a microwave usage, otherwise I wouldn't use a 2nd battery
 

Lightflyer1

Top Post Dawg
Joined
Sep 13, 2005
Location
Round Rock, Texas
TDI
2015 Beetle tdi dsg
A cooking microwave? That would also require about a 2k watt inverter. By the time you get those you could have a small generator to power that. It would be a lot better than your batteries in my opinion. Also useful for other things. I picked up a small Honda generator (2k watt) off CL for $300. Your alternator isn't made for replacing huge amounts of energy drawn from your batteries. If they go flat it is best to use a wall charger to re energise them, not your car charger. That inverter/microwave setup will have a heck of a draw down on both batteries causing your alternator to work really hard to replace it. Bad idea unless there is absolutely no other alternative.
 

iamatt

Veteran Member
Joined
Apr 5, 2006
Location
Rosharon, Texas
TDI
2014 Jetta 6 Speed manual
Just get a Honda 2200i generator. You are doing some pretty weird **** to run a microwave. I see more over thought stuff done on this board than anywhere else for some reason :)

Sent from my Pixel 3 using Tapatalk
 

Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
COLORADO (SE of Denver)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress) I moved so now i got nothing but an AHU in a garage on a pallet.
Run a microwave?
Forget the extra battery. You will be better off sticking your microwave boritos on the clove cover for an hour
 

turbobrick240

Top Post Dawg
Joined
Nov 18, 2014
Location
maine
TDI
2011 vw golf tdi(gone to greener pastures), 2001 ford f250 powerstroke
I can see a new "As seen on TV" product- the tailpiping-hot mini roaster. Just slip one end into the tailpipe and let the patented heat exchanger do the rest.
 

Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
COLORADO (SE of Denver)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress) I moved so now i got nothing but an AHU in a garage on a pallet.

MAXRPM

Veteran Member
Joined
May 7, 2008
Location
US
TDI
00 Jetta and 99.5 Golf, 2015 Passat TDI,BMW 2
Jesus Christ, I got a 2k inverter and if I use 2 batteries the small microwave works I tested it, even with one battery and the inverter works but I could see that alternator and supply V are suffering, c'mon guys stop flaming the thread, reason I need a sealed battery is be cause I do not want fumes coming out of the lead acid battery from trunk and smelling that, so getting with the topic, I am reading that I can hook it up and others saying I can't.

If I can't Plan B probably would be to buy a lead acid battery with breather little hoses hooked up from the top of the battery and route them to the outside,my 335D got battery like that in the trunk
 
Last edited:

Lightflyer1

Top Post Dawg
Joined
Sep 13, 2005
Location
Round Rock, Texas
TDI
2015 Beetle tdi dsg
If you read the link I posted you will see that the two different battery types are not compatible at least charging wise. They each need a different type of charging scheme. I think our cars are even capable of switching between the two. But you can't have 2 different types of batteries and use one setting for charging them both. Either two AGM or two LA and set the charging scheme for the type you pick. Even modern chargers now have a switch to pick LA, deep cycle or AGM types. Still not a very good idea to do in my opinion.
 

turbobrick240

Top Post Dawg
Joined
Nov 18, 2014
Location
maine
TDI
2011 vw golf tdi(gone to greener pastures), 2001 ford f250 powerstroke

Nah, that's just a glorified mess kit. I had one in scouts. The mini roaster patented heat exchanger is where the magic happens.

What sorts of items are you planning to nuke? Frozen dinners? A little hibachi grille and some charcoal would be my preference for most cooking. The cheap little burners that screw onto propane camping cylinders work well too.
 

MAXRPM

Veteran Member
Joined
May 7, 2008
Location
US
TDI
00 Jetta and 99.5 Golf, 2015 Passat TDI,BMW 2
I believe I saw at costco batteries H6 with AGM stickers on the side, and I think that's the battery for the 2.0 tdi passat. I'm not too sure I'm going to go back and check.
 

MAXRPM

Veteran Member
Joined
May 7, 2008
Location
US
TDI
00 Jetta and 99.5 Golf, 2015 Passat TDI,BMW 2
Need 2 batteries for several things, cooler running 6 to 10 hrs, 2 accumulators will work better than 1 , warming up food, coffee, running lap top, and so on
 

Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
COLORADO (SE of Denver)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress) I moved so now i got nothing but an AHU in a garage on a pallet.
Even an AGM battery needs to be properly vented.
What? No. They are 100% completely sealed. They dont need to breath much externally as they dont really heat up much at all. The entire reason for AGM is to NOT dump acid into a lake when your fishing boat tips over.
 

turbobrick240

Top Post Dawg
Joined
Nov 18, 2014
Location
maine
TDI
2011 vw golf tdi(gone to greener pastures), 2001 ford f250 powerstroke
Last edited:

Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
COLORADO (SE of Denver)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress) I moved so now i got nothing but an AHU in a garage on a pallet.
Well then. The more you know. They dont specifically require it be vented to outside. Just the room it's in. Aka a fart fan will do.
 
Last edited:

turbobrick240

Top Post Dawg
Joined
Nov 18, 2014
Location
maine
TDI
2011 vw golf tdi(gone to greener pastures), 2001 ford f250 powerstroke
They require venting, just as JM said. A trunk is an enclosed area. Nobody here is talking about rooms.
 

Vince Waldon

Top Post Dawg
Joined
Apr 25, 2009
Location
Edmonton AB Canada
TDI
2001 ALH Jetta, 2003 ALH Wagon, 2005 BEW Wagon
Perhaps even more important, starter batteries are optimized for delivering short bursts of high current and will rapidly degrade in situations where they are being asked to deliver medium amounts of current for long periods of time, AGM or conventional. Not what the plates are designed for.

Instead, the application the OP is describing might be best served by a deep-cycle battery... and best charged thru a battery isolator, so that both batteries can charge on their own but also discharge on their own.
 

Lightflyer1

Top Post Dawg
Joined
Sep 13, 2005
Location
Round Rock, Texas
TDI
2015 Beetle tdi dsg
Need 2 batteries for several things, cooler running 6 to 10 hrs, 2 accumulators will work better than 1 , warming up food, coffee, running lap top, and so on
This is best served by a small generator, not batteries. As I said I picked up one of these Honda EU2200i generators for $300 a year or so ago. Great for things like you stated and power outages to keep the refrigerator and phones and lights going. Or outings where power is needed. Quiet too and fuel efficient. I would be looking for a good deal on one of these instead. Your battery(s), inverter setup will have some real issues for what you are doing.

https://powerequipment.honda.com/generators/models/eu2200i
 

VicGuy

Veteran Member
Joined
Dec 31, 2019
Location
Victoria BC
TDI
2012 JSW Golf Wagon, 97 Golf Turbo Diesel
Perhaps even more important, starter batteries are optimized for delivering short bursts of high current and will rapidly degrade in situations where they are being asked to deliver medium amounts of current for long periods of time, AGM or conventional. Not what the plates are designed for.
Instead, the application the OP is describing might be best served by a deep-cycle battery... and best charged thru a battery isolator, so that both batteries can charge on their own but also discharge on their own.
This ^^^^^ is just what I was thinking also.

You'll get good advice if you take this question to a boating forum where dealing with 'starting' and 'house' batteries is very common.

BTW, I saw my Mom/Dad heating the baby bottle (they must have wrapped it in a cloth?) on the engine manifold in the 1950s, so nothing new about that concept!
 

Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
COLORADO (SE of Denver)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress) I moved so now i got nothing but an AHU in a garage on a pallet.
They require venting, just as JM said. A trunk is an enclosed area. Nobody here is talking about rooms.

Neither of these pertains to a trunk at all.
All the codes listed were to do with stationary rooms or fully sealed areas.
The trunk of a car is NOT sealed. If it was then you would suffocate if stuck inside.
It’s been a standard code since the late 90's, maybe earlier, that you can get out of the trunk of any car from within and/or that it is able to exchange enough air to not suffocate.
HENCE it’s not an area that would be considered not ventilated. Besides hydrogen is MUCH lighter than air and would escape though the speaker deck or rear seat much faster than is needed.
People have been putting AGM's in trunks for decades and have never had to add ventilation or any nonsense like this. HECK, in some cars, they have an AGM battery UNDER the front seat.
FFS making this into a big deal over such a stupid thread anyways.
WHO THE HECK cares if someone puts an AGM battery in the back of a CAR to run a MICROWAVE.
Reminds me of this every time i see this thread.
 
Last edited:

turbobrick240

Top Post Dawg
Joined
Nov 18, 2014
Location
maine
TDI
2011 vw golf tdi(gone to greener pastures), 2001 ford f250 powerstroke

Neither of these pertains to a trunk at all.
All the codes listed were to do with stationary rooms or fully sealed areas.
The trunk of a car is NOT sealed. If it was then you would suffocate if stuck inside.
It’s been a standard code since the late 90's, maybe earlier, that you can get out of the trunk of any car from within and that it is able to exchange enough air to not suffocate.
HENCE it’s not an area that would be considered not ventilated. Besides hydrogen is MUCH lighter than air and would escape though the speaker deck or rear seat much faster than is needed.
People have been putting AGM's in trunks for decades and have never had to add ventilation or any nonsense like this. HECK, in some cars, they have an AGM battery UNDER the front seat.
FFS making this into a big deal over such a stupid thread anyways.
WHO THE HECK cares if someone puts an AGM battery in the back of a CAR to run a MICROWAVE.
Reminds me of this every time i see this thread.
Just because you and I have no need for a vehicular microwave doesn't make the OP stupid for wanting one. I find it insulting that you would suggest that.

If you actually bothered to read your little snippet, you'd have seen that tightly enclosed spaces are included as requiring venting. In bold print with an exclamation point, no less. I guarantee that all modern vehicles equipped with a lead acid battery in the passenger compartment or trunk from the factory have a means to vent hydrogen gas. Typically, it's a simple plastic tube that attaches to the vent on the top of the battery/battery box and is routed outside.
 
Last edited:
Top