Second Battery Gremlins

[SameGuy]

Below is a diagram of how I have my second battery and my accessories wired up in my 2012 Tundra. Yes I know, everyone wants their winch and compressor wired to their house battery but these things don't run when the engine is not on so lets not worry about that right now.

I am tracing down a possible parasitic drain so decided to remove the accessories from the negative terminal one by one and measure between those terminals and the batteries negative. The winch and compressor showed no voltage, however the negative wire that connects the house and starter battery directly (2GA wire) showed 3.2 volts running through it. The Blue Sea ACR was in disconnect while testing this and the starting battery was reading 12.4 volts resting. There was nothing connected to either 12 volt plug in the cab or bed. The ACR seems to be working as it should, the house battery showing 12.7 volts resting and charges fine after use, disconnects as it should etc. (this setup has been working fine for over a year)

SO I am most curious about this mysterious 3.2 volts between the 2 negative battery terminals. Could the ACR be having some bleed through? Doesn't seem possible as I have measured each terminal on the ACR to ground and got 12.7 volts (house battery) and 12.4 volts (starting battery) respectively. (with ACR in disconnect)

My relatively new Optima may be faulty, I'm going to have it tested this afternoon, and there is a possibility that my remote start is draining the battery. Odd thing is after a few days it shows 11.6 volts but starts without hesitation which sounds impossible to me. I don't think the ACR is combining the batteries when the starting battery is low, I wouldn't think it would do it on its own.

Any wisdom from the 12 volt experts would be greatly appreciated.

 

[Hillbilly Heaven]

Do the measurement you just did with the negative between the two batteries disconnected. Remember that voltage do not assume it is the same 3.2 volts you measured earlier. Now with negative between them disconnected measure each battery at the battery terminals. I will bet you a cookie the difference between the two batteries will be the same as what you measured when you measured negative to battery. You should be able to isolate both batteries from each other manually with the ACR knob. Charge the batteries up and see if it still drains the battery when in manual off position.

 

[Ducky's Dad]

I am curious as to where you mounted the second battery. There does not seem to be a good spot in my 2008 Tundra.

 

[SameGuy]

The plot thickins....... I had the battery tested at the auto parts store, not the one I bought it at. Battery tested good so the low voltage issue is some parasitic draw that I will track down, not too worried about that, I'll find it.

HH, I tested everything again and here's what I got:
at the terminals, ground removed between batteries, ACR in disconnect
Starting battery 12.3v
House battery 12.6v
Ground of starting battery to ground wire to house battery 2v
House side of ACR to Ground 10.5v
Starting side of ACR to Ground 12.3v
inside cab outlet 10.5v
truck bed outlet 12.5

I'm still not understanding why I am loosing roughly 2 volts between the house side of the ACR and the truck ground, and why I am getting 2 volts between the two battery neg. terminals. Is is because the house battery is only grounded through the starting battery then to the frame? I never noticed this before when I had the two negative battery terminals connected.

Should I ground the house battery neg. terminal to the frame, or is this even something to worry about? I mean in reality, it is grounded to the frame, but through 20+ ft of 2 ga wire and the starting battery.

 

[SameGuy]

I am curious as to where you mounted the second battery. There does not seem to be a good spot in my 2008 Tundra.

I had a fabricator build me a battery mount that goes under the bed of my truck, it is really slick. It pivots down to slide the battery in and wire it up, then bolts into place on the drivers side. Think I paid $200-300 for him to think it up and install it. First shot from the passenger side, second from the drivers. Sorry the pictures are lacking, its a little wet outside to crawl underneath.

 

[Ducky's Dad]

That is slick, although a bit hard to get to without a lift. I put a pair of G34 boxes on the frame rail of my Dodge and now I wish I had put in something bigger. My Tundra has a Northstar G31 in the engine compartment, but I still feel better with two batteries.

 

[Hillbilly Heaven]

What did you have plugged into the power outlets at the time of your measurements and do the power outlets have illumination?

 

[Hillbilly Heaven]

The plot thickins....... I had the battery tested at the auto parts store, not the one I bought it at. Battery tested good so the low voltage issue is some parasitic draw that I will track down, not too worried about that, I'll find it.

HH, I tested everything again and here's what I got:
at the terminals, ground removed between batteries, ACR in disconnect
Starting battery 12.3v GOOD
House battery 12.6v GOOD
Ground of starting battery to ground wire to house battery 2v BAD should have been 0 Volts. This is called a ground differential. All ground points should measure 0 volts between each point. You should only have one main ground point.
House side of ACR to Ground 10.5v BAD should have measured 12.6 volts
Starting side of ACR to Ground 12.3v GOOD
inside cab outlet 10.5v BAD but was expected considering House Side ACR to Ground
truck bed outlet 12.5 GOOD
I need some sleep to sort this thru my head. It is probably right in front of my face.
I'm still not understanding why I am loosing roughly 2 volts between the house side of the ACR and the truck ground, and why I am getting 2 volts between the two battery neg. terminals. Is is because the house battery is only grounded through the starting battery then to the frame? I never noticed this before when I had the two negative battery terminals connected.

Should I ground the house battery neg. terminal to the frame, or is this even something to worry about? I mean in reality, it is grounded to the frame, but through 20+ ft of 2 ga wire and the starting battery.

Replies are in red.

 

[Ducky's Dad]

"Starting battery 12.3v GOOD
House battery 12.6v GOOD "

I'm not sure either of those is good. I think one of OP's batteries is an Optima, and full charge on those is either 13.1V or 13.2V, depending on whether it is a Starting battery (Red chemistry) or a dual purpose (Yellow chemistry). Both 12.3 and 12.6 would be pretty depleted for an Optima.

 

[Umbrarian]

"Starting battery 12.3v GOOD
House battery 12.6v GOOD "

I'm not sure either of those if good. I think one of OP's batteries is an Optima, and full charge on those is either 13.1V or 13.2V, depending on whether it is a Starting battery (Red chemistry) or a dual purpose (Yellow chemistry). Both 12.3 and 12.6 would be pretty depleted for an Optima.

Agreed. From OPTIMA:

Fully-charged, our REDTOP batteries (and 34M BLUETOP) will measure about 12.6-12.8 volts and our YELLOWTOP and BLUETOP (except the 34M) batteries will measure about 13.0-13.2 volts. Each manufacturer will generally indicate a range or minimum voltage level for a fully-charged battery. If you are measuring the voltage on another brand of battery and don't know what the fully-charged voltage level should be, it is safe to assume it should be at least around 12.6 volts

https://www.optimabatteries.com/en-us/experience/2013/12/how-do-you-measure-battery-voltage

 

[SameGuy]

What did you have plugged into the power outlets at the time of your measurements and do the power outlets have illumination?

nothing plugged into the power outlets and no illumination. The ground between the two batteries is still disconnected at this point with these readings. When it is connected, the house side of the ACR to ground is 12.6v, and the inside cab outlet also reads 12.6v.

 

[SameGuy]

Agreed. From OPTIMA:

Fully-charged, our REDTOP batteries (and 34M BLUETOP) will measure about 12.6-12.8 volts and our YELLOWTOP and BLUETOP (except the 34M) batteries will measure about 13.0-13.2 volts. Each manufacturer will generally indicate a range or minimum voltage level for a fully-charged battery. If you are measuring the voltage on another brand of battery and don't know what the fully-charged voltage level should be, it is safe to assume it should be at least around 12.6 volts

https://www.optimabatteries.com/en-us/experience/2013/12/how-do-you-measure-battery-voltage

The Starting battery is an Optoma Yellowtop D35, the house battery is a CHEAP 100AH deep cycle FLA. There is some parasitic drain causing this low voltage issue with the starting battery, this I'm sure of. To top it off I think I have probably driven 15 miles in the past two weeks, the downfall of living 1/4 mile from work. Hopefully this afternoon I'll get a chance to charge it up fully and trace the drain once I figure out how to disconnect the remote start. The House battery from new rests at 12.7 volts so I think I'm ok there.

 

[luthj]

A few thoughts.

What is your alternator voltage (engine running at the battery)?

You are going about this the wrong way. Measuring voltage with stuff disconnected won't do you much of anything. You want to measure current. Generally most multi meters can measure up to 10A. So set the meter to the current/amp setting, move the leads to the right plugs if needed. Disconnect the load you think is parasitic, and use the meter to complete the circuit. This could be at the ground/negative, or at the positive side of the loads supply wires.

The ML-ACR has a standby power usage of around 13mA. I am not sure which battery (or both) this is split between when the ACR is open. The trucks electronics will use 50-150mA depending on options (remote entry, etc). You may be able to measure the standby power usage, sometimes reconnecting the battery will cause a short term current to peak over 10A and blow the meters fuse (not a big deal). Depending on the size of your starting battery, the vehicles standby power consumption will draw the battery down as much as 25% every 10 days. Possibly even more.

Resting voltage alone is not the best way to measure battery health. The alternators on toyotas are generally 13.8-14.0V or so. Which is suitable for keeping a starting battery topped up with some regular driving. It won't fully recharge a deeply cycled battery. So a once a week charge with a quality shore power charger is recommended. This means several hours being held at the absorb voltage, which is usually 14.4-14.6V but can be higher.

 

[bajavanadu]

Please excuse the dumb question, but why is the ground on the second battery connected to the ground on the starting batt? On my rig, I grounded my second batt on the frame next to the mount. Did I wire up my second batt incorrectly?

 

[SameGuy]

A few thoughts.

What is your alternator voltage (engine running at the battery)?

You are going about this the wrong way. Measuring voltage with stuff disconnected won't do you much of anything. You want to measure current. Generally most multi meters can measure up to 10A. So set the meter to the current/amp setting, move the leads to the right plugs if needed. Disconnect the load you think is parasitic, and use the meter to complete the circuit. This could be at the ground/negative, or at the positive side of the loads supply wires.

The ML-ACR has a standby power usage of around 13mA. I am not sure which battery (or both) this is split between when the ACR is open. The trucks electronics will use 50-150mA depending on options (remote entry, etc). You may be able to measure the standby power usage, sometimes reconnecting the battery will cause a short term current to peak over 10A and blow the meters fuse (not a big deal). Depending on the size of your starting battery, the vehicles standby power consumption will draw the battery down as much as 25% every 10 days. Possibly even more.

Resting voltage alone is not the best way to measure battery health. The alternators on toyotas are generally 13.8-14.0V or so. Which is suitable for keeping a starting battery topped up with some regular driving. It won't fully recharge a deeply cycled battery. So a once a week charge with a quality shore power charger is recommended. This means several hours being held at the absorb voltage, which is usually 14.4-14.6V but can be higher.

At Idle, with both batteries a little lower than they should be, my clamp on Amp meter showed 24-30 Amps going into the battery. I had the charging system checked when I had the battery tested and its up to par. I know there is a parasitic draw coming from the remote start, and the regular systems on the truck. It's not something I am not overly concerned about it, and haven't had the chance to check it specifically, but will here this weekend. I'll probably wind up putting a manual switch in it for when the truck sits for long periods. I ordered a little Optima battery charger to top off and maintain the batteries in situations like this to keep them happy, probably use them every couple weeks if I'm not driving enough. I'm still puzzled by the ground differential issue but I don't feel like it is that much of a problem, this system has been working just fine for over a year. The long term solution may be to get a small solar panel mounted on the roof to trickle charge. Probably not that necessary as my rig rarely sits unused for more than a few days at a time.