Dual Battery System Killed Main Battery

I'm not 100% sure, but now that I think about it on Monday I was running a shop vac off the aux battery and actually ran it to the point where the vac didn't run anymore. The next day is when I started having problems. The reason I assumed it may be the DBS is based on what I vaguely remember reading. I'm wanting to say it had to do with draining the battiers when you have different batteries or something, which would jive with my situation.

In terms of your questions:

• Main battery is what came with the truck and I bought it brand new last March.
• Bench charge is in process
• After bench charge I will be bypassing the DBS.

I'll report back.

Thanks for the help man!

 

Speaking as an engineer with two degrees in the field... the issue is that if there is any voltage difference between the two batteries, they will equalize. The higher voltage battery will try to charge the lower voltage battery, until the voltage of the two is equal. Once the voltage is equal, there can be no further bulk movement of electrons and everything is stable.

In the case of having two conventional batteries or two AGM batteries, this is typically fine. However, mixing two types of batteries WILL cause one or the other to drain somewhat. Not *completely*, but a bit. AGM batteries, for example, are a few points of a volt higher than conventional batteries, so they should NOT be mixed without being isolated.

The short term effect of mixing a conventional and AGM battery in parallel, is that the AGM battery will not remain at a state of full charge. The long term effect is that the life of *both* batteries will be slightly reduced. Probably not noticeably though.

The "big problem" of keeping batteries hooked up in parallel comes in when one of the batteries is degraded and unable to hold a complete charge as well as the other. In this case, it will pull the other battery down with it. The greater the degradation, the greater the voltage difference, and the faster it will pull the other battery down. In worst case, the bad battery could actually kill the good battery by discharging it too deeply or too quickly.

When hooking up two batteries in parallel to a single charger (alternator), it really is important to use a proper isolation circuit. The alternator output regulator keeps the output voltage at a sensible level for maintaining the batteries, so this isolation circuit could be as simple as splitting the alternator output through two high power diodes -- one to each of the two batteries. This will prevent reverse flow from one battery over to the other. I.e., alternator --> input_diode1 --> battery1, current only flows *into* the battery.

Similarly, if your objective is to keep the batteries in parallel to boost current on the same circuit, the output from the batteries should be only joined after each running through a diode. I.e., battery1 --> output_diode1 --> output circuit. There must be no connection between alternator and output circuit.

This setup with 4 high power diodes will allow the two batteries to be kept in parallel without affecting each other.

Note: diodes that are big enough for that output circuit do not come cheap. They need to each be able to handle about 2 kA (i.e. twice the battery's rating). Anybody interested in trying out a circuit like this should consider rigging up multiple smaller diodes in parallel since you can pick up a 500 amp diode for a few bucks. For example http://ca.mouser.com/ProductDetail/...=sGAEpiMZZMtoHjESLttvkvsK1VtXAMYYKrDn63S0XSc=

 

In case you haven't read everything fully, we ARE talking about running a system with a full isolator, which negates your first argument of one battery discharging into the other. As long as the vehicle owner does not tie any power circuits between the two, it will not matter what type of batteries they run on primary and secondary. The discussion is to NOT have two batteries hooked in parallel. All of my DBS systems have a solid state isolator capable of doing the job. My jump start option simply uses a high current solenoid that temporarily connects the secondary battery to the primary battery so that one can start their own truck with a single switch flip.

 

Well, OP actually indicated that what he is using is not "your" configuration. Either way, what I wrote describes why and how things interact, it isn't an attack on anything you sell, so I'm not sure why you are responding with that kind of hostility.

 

Any hostility felt is self-made. None intended at all. Was simply clarifying what the discussion was around as I have been trying to help to OP get his issue sorted out.

 

Ok then. FYI, the way you emphasized some works came out as hostile.

 

Not intended.

 

Good morning Gents,

Thanks a bunch for all the replies. I just got back from a trip to the Eastern Sierras last night so I haven't had a computer to reply. That said, here's some updates:

The dealership agreed the battery was toast and swapped it out for me so now I've got a brand new one in there which got me through my trip safely.

In terms of battery isolation, what I use for my DBS is made by IBS (http://ibs-tech.ch/en/products/dual-battery-system/ibs-dbs.html). I run their relay booster module as well. What are your thoughts on the quality of this? Can I expect those batteries to eat at each other when I turn my truck on and both are charging? My understanding would be no based on what I read, but please correct me if I'm wrong. Now assuming as much, it begs the following question:

Now I may have had my key in the "On" position, but without the engine running, the day I drained my aux battery (right before the main battery died). This links the two batteries together if I understand the way the IBS DBS works. That said, based on what @tgear.shead stated, is it safe to say that even with a solid battery isolator, when the two are linked for reasons other than charging (like when I had the truck key "On" but no charge coming from the alternator), I can anticipate them to destroy each other, correct?

 

The IBS system is not a true isolation system. Thus you can expect issues to be possible by what Tgear said. Only a true isolation system diagrammed in post #16 will protect the batteries from each other. This is why I have always suggested AGAINST using the IBS systems. They just don't TRULY have a isolation between the batteries. Check my 1st gen and 2nd gen electrical upgrade threads and you can read a lot more about how a true isolation system is key.

 

Okay, so given that I'm pregnant with this situation now that I've dumped $500 into the IBS, will getting a matching optima be my best option aside from unloading another ~$500 on a different isolator? I'll be reading your posts and it sounds like I'll end up getting a system from you when I do my wife's jeep (assuming it works, which I assume I'll find out now when I read)

 

I had an issue with one of my batteries a month ago. Found out that my winch had a power wire that had a short. Every time that power wire hit some metal, it activated the winch. Did this two nights in a row and my primary battery was dead two days in a row before finding this problem. So it could be something similar. Hope that helps.

 

A Battery Isolator Solenoid shouldn't be more than $100. Like @BamaToy1997 said the IBS isn't a isolation system, to me it just seems to be a very expensive battery gauge.

 

In the case of an IBS system, you do need to have matching batteries since they are not a TRUE isolation system.

A battery isolator solenoid is exactly what IBS uses, and it is not a true isolator. A TRUE isolator uses a solid state heavy duty diode system, which is what my Kits have. Those isolators run between $140 and $200 depending on the amperage.