Dual Battery setup with different batteries

[AlexJet]

Odysseys are nice. They are just about the only ones who make a thin plate cranking battery that is also rated for deep cycle use.

Note in the specs on the PC1500 that it can handle 400 cycles to 80% discharge. That's the lifecycle. That means you can drain it 80% 400 times and then you'll probably have to replace it. All lead-acid batteries are like that. The deeper you go, the less cycles you'll get. That same battery could probably do 3000 cycles if you only drained it 25%. You'd probably get 10,000 cycles if you only drained it 5% or less for engine starting.

If you intend to run auxiliary loads with the engine off, then you should go with a standard aux battery setup - use an isolator to charge the second battery when the engine is running, and isolate the batteries when the engine is not running. Then attach your aux loads to the aux battery so you don't drain your engine battery while running those aux loads.

For a winch, I would hook the winch up to the engine battery to supply heavy amps under load, and allow the aux battery to help out as needed. The engine will probably be running in that situation so the alternator will help out as well. (Well...I would with normal batteries. With Odysseys, it probably doesn't matter which battery you hook the winch up to as long as the battery cables between them are heavy enough to handle the amps.)

All other aux loads should go to the aux battery.


If you hook up your aux loads to the engine battery and run it down, then the aux battery is basically useless except to maybe jump start the truck when you need to, and to help out when running the winch.

As far as charging, the only difference in those batteries you listed is the capacity. They all accept exactly the same charge parameters. The charging specs are described in the Odyssey Tech Manual:

http://www.odysseybatteries.com/files/US-ODY-TM-001_0411_000.pdf

In other words, with those Odysseys, being charged from a vehicle's charging system, you can mix and match them to your heart's content.


Also, keep in mind that even 68 amp*hours is not a hell of a lot when talking about running aux loads for days while camping. If you want a lot of cycles (long life) from those expensive batteries, then don't drain them below 50% - which means that you'd actually have 34ah available.

Thanks for your comments. Very helpful notes. I'm not using much power when the engine is off. It may be just running the radio (I don't have subwoofers or amplifiers, just basic radio) and couple lights to light up the camping sites (want to replace my halogen fogs with LEDs, so they can drain less).

 

[dwh]

Thanks for your comments. Very helpful notes. I'm not using much power when the engine is off. It may be just running the radio (I don't have subwoofers or amplifiers, just basic radio) and couple lights to light up the camping sites (want to replace my halogen fogs with LEDs, so they can drain less).

Well, if that's all you are doing, then there is another alternative - low-voltage disconnect. That basically lets you run loads from your starting battery until your battery starts getting low, then disconnects the loads so the battery always has enough charge to start the battery. There are lots of different kinds of LVD. This one's kinda sexy:

http://www.batterystuff.com/battery-products/PS12VMarine.html


Battery Brain is another sort:

http://www.youtube.com/watch?v=yECwvd1Qhtg

 

[MobTuff]

Odysseys are nice. They are just about the only ones who make a thin plate cranking battery that is also rated for deep cycle use.

Note in the specs on the PC1500 that it can handle 400 cycles to 80% discharge. That's the lifecycle. That means you can drain it 80% 400 times and then you'll probably have to replace it. All lead-acid batteries are like that. The deeper you go, the less cycles you'll get. That same battery could probably do 3000 cycles if you only drained it 25%. You'd probably get 10,000 cycles if you only drained it 5% or less for engine starting.

If you intend to run auxiliary loads with the engine off, then you should go with a standard aux battery setup - use an isolator to charge the second battery when the engine is running, and isolate the batteries when the engine is not running. Then attach your aux loads to the aux battery so you don't drain your engine battery while running those aux loads.

For a winch, I would hook the winch up to the engine battery to supply heavy amps under load, and allow the aux battery to help out as needed. The engine will probably be running in that situation so the alternator will help out as well. (Well...I would with normal batteries. With Odysseys, it probably doesn't matter which battery you hook the winch up to as long as the battery cables between them are heavy enough to handle the amps.)

All other aux loads should go to the aux battery.


If you hook up your aux loads to the engine battery and run it down, then the aux battery is basically useless except to maybe jump start the truck when you need to, and to help out when running the winch.

As far as charging, the only difference in those batteries you listed is the capacity. They all accept exactly the same charge parameters. The charging specs are described in the Odyssey Tech Manual:

http://www.odysseybatteries.com/files/US-ODY-TM-001_0411_000.pdf

In other words, with those Odysseys, being charged from a vehicle's charging system, you can mix and match them to your heart's content.


Also, keep in mind that even 68 amp*hours is not a hell of a lot when talking about running aux loads for days while camping. If you want a lot of cycles (long life) from those expensive batteries, then don't drain them below 50% - which means that you'd actually have 34ah available.

I'm thinking of putting in a large amp hour battery that would be auxiliary to my starting battery. My main starting battery is a smaller Sears Platinum AGM starting battery and the aux battery will be a deep cycle 210 amp hour AGM. My main concern is how different each battery will be. Especially the difference in amp hours. If I install for example the National Luna Intelligent Solenoid I should not have to worry about the batteries trying to equalize?

 

[DaveInDenver]

Also, keep in mind that even 68 amp*hours is not a hell of a lot when talking about running aux loads for days while camping. If you want a lot of cycles (long life) from those expensive batteries, then don't drain them below 50% - which means that you'd actually have 34ah available.

I know dwh knows all of this, I'm just quoting him for context and to add a bit of detail since I run a pair of PC1400 batteries, rated at 65 A-hr. Batteries are rated to a minimum voltage and Odyssey bases their spec on 10.02V as the cut-off. I use 11.0V as the low voltage cut off on the aux battery, based on my Engel which won't run below 10.5V. This usually lets me extract roughly 50 A-hr, which is about 75% or 80% of capacity. In the summer 2 days is pushing it with the fridge running as much as 50% duty during the day.

They perform quite a bit better than the Red Top for small loads but they aren't going to mistaken for a real deep cycle. I've never owned a Yellow or Blue Top to compare. The PC1400 65 A-hr seems about right. I think I could get close to the full 65 if I was to run all the way to ~10V, but that last 0.5V isn't useful to me since nothing will run that low. The fridge is unreliable, my radios turn off, etc. I can get about 55 A-hr if I cut off at 10.5V, which is about 85% state of discharge.

I actually just tested this last month, letting the fridge run on the battery. Took 5 days (that was just the length of time I had) to get to 11.6V but my duty cycle was about 15% (fridge ran maybe 10 minutes per hour) so I ended up only pulled about 37 A-hr from it. My batteries, though, are in good shape and still young so long term aging is still yet TBD. They're about 18 months old and the aux battery only has a handful of cycles. It's only been run down to 11V a couple of times (I estimate 3) and total number of discharges even close to 12V is probably on the order of a dozen. Odyssey rates their batteries for 400 cycles, so I should be maybe still within a few percent of new. My ML-ACR usually doesn't disconnect them until the next time I turn on the truck to start it, so they're holding up ~12.7V well, for around 12 hours at least even with the parasitic load.

The main thing is it looks like Odysseys seem to recover well from deep discharges, particularly if you do routine maintenance charges. All batteries benefit from putting them on a good 3-stage charger once in a while. The voltage that our vehicle charging systems use is good for putting a charge back in quickly and is safe for floating with a small load while running. It's neither ideal for a true float or true bulk or absorption, though. So using a charger that can do a bulk at ~14.7V and taper to absorption and float, followed by a day or two at ~13.8V every month or two can significantly help maintain your battery life.

By only using the vehicle charging you are only achieving perhaps a 98% recharge and over time the capacity reduces. This will happen to all batteries. If you run down and return short by a percent or two every time you're just leaving capacity and life on the table. It's not quite as obvious on a starting battery because starting a car is actually not very difficult on it so you're using only consuming a fraction of life. But with a house battery that you draw down to 50% each time this can be significant very quickly.

In fact Odyssey states that the 400 cycles requires charging to 14.7V. When only charged to 14.2V their batteries will only get on the order of 50 to 100 cycles. I always put my aux battery on a long maintenance charge after a trip that takes them into deep discharge because of this. Now this is doing deep discharges to 10.02V (IOW, 100% discharges) in their test. They did 4 sample batteries and even doing full 14.7V one sample only got 250 cycles anyway, so it's a very harsh test. One sample did get 350 cycles before capacity was lost, though. There were using a 2.3A load, so it's similar to running a fridge at 100% duty cycle.

One reason I mention this is there is mention of using diode isolators. You have to be aware that isolating your batteries with diodes will result in some voltage drop, so you have to know the terminal voltage of your batteries. IOW, if your voltage bus is 14.4V normally and you put in a 0.7V drop diode (which is about as bad as can be) then your batteries are only seeing 13.7V. This is very bad for them since they will never bulk charge. If you're isolating both batteries you can adjust the voltage regulator up to account for this. If you can't or both batteries are not at the same potential, then you need to make sure to find an isolator with as small of a diode drop as possible and be sure to periodically charge. If you're doing solar to the aux battery and only relying on the vehicle for back up then it's may never be an issue. But just be sure to check.

 

[Ducky's Dad]

The main thing is it looks like Odysseys seem to recover well from deep discharges, particularly if you do routine maintenance charges.

In my experience with a bunch of Odysseys, that is true of the 1500s (G34 and 34/78) but not of the 2150 (G31). I am on my third 2150, have an Odyssey charger as well as a Ctek and an Optimus (not Optima), and even with reconditioning charges every two-three weeks, I can't keep the 2150 happy. Can't even get it to hold a full charge (12.84OCV) overnight. For over a year I kept a detailed log on my current 2150, with mileage, dates, shore power charge cycles, charge voltage at end of reconditioning cycle, state of charge after disconnecting charger, OCV after overnight rest, and ambient temps. The 2150 always settles in at about 12.65OCV after reconditioning, no matter what I do. And 12.65 is far from a 100% state of charge. Frustrating is an understatement.

 

[DaveInDenver]

Interesting to hear. I've been pretty happy with my PC1400. I'd have thought the construction and materials would have the main difference.

 

[dwh]

I'm thinking of putting in a large amp hour battery that would be auxiliary to my starting battery. My main starting battery is a smaller Sears Platinum AGM starting battery and the aux battery will be a deep cycle 210 amp hour AGM. My main concern is how different each battery will be. Especially the difference in amp hours. If I install for example the National Luna Intelligent Solenoid I should not have to worry about the batteries trying to equalize?

Smart solenoid isolators connect the batteries while they are being charged, and disconnect them when they aren't being charged.

So the difference in amp*hours doesn't matter, and no, the batteries don't sit around trying to equalize.

No worries.

 

[coop74]

have you considered a DC to DC charger? it will keep the battery up and you can choose any type and size battery you might want...