so i spent lots of time reading today about this and even called hellroaring (very nice and helpful on the phone).... here's what i come away with for those that may want lots of info before making a decision:
there are 5 types of battery management systems that i count...
1. a manual high-current switch with A/B/BOTH selectors (a "boat switch")- there are no "smarts" to the system, it only does exactly what you tell it, this can be good and bad (good that you have full control, but bad as you could leave it set to "both" and leave something on thereby depleting both batteries and having no backup)
- when in "both" mode, the batteries are not isolated in any way, i.e. if one is a different physical type that rests at a lower voltage, it will always be trying to discharge the higher resting voltage one
- good in the fact that you wouldn't have to remove a completely shorted battery physically from the system. i.e. you could just set the switch to "B" if "A" had completely shorted out.
- doesn't work well remotely... i.e. you need to mount the switch near the batteries or else you are going to have to run 3 cables of some very large gauge wire all the way to wherever the switch is (i've seen it done, but not practical for most people)
2. a "boat switch" and a battery isolator (such as from sure power or perfect switch)- all the same characteristics as just a "boat switch" but without the worry of one battery "bleeding" the other, the batteries are isolated in that only charge current goes to both of them, but no current transfers between them
- i my opinion this would always be the way to go in a completely manual system, you wouldn't want to just go with the boat switch when you can pickup and isolator to use with it for pretty cheap
3. an intelligently controlled solenoid system (national luna or IBS for example)- in this case a solenoid (high current relay) acts as the "boat switch", except in all systems i know of, you only have "A" and "BOTH" settings. the big plus is that you run a small cable to a remote controller to set the state of the solenoid instead of having to run giant cable in order to relocate the "boat" switch (and the solenoid stays near the batteries).
- the intelligence is in the form of a small microcontroller that can monitor either ignition state and/or time and/or each battery's voltage, and based on that information set the solenoid switch to "A" or "BOTH"
- - when i say monitor ignition-state/time/voltage, it depends on the system. some merely tie the batteries in parallel (i.e. the "BOTH" setting) when the car is running and for a few moments after the car has been shut off, then it sets everything back to the main battery (i.e. the "A" setting). other systems may be smarter and actually look at each batteries voltage and the incoming voltage and sense that it's ok to tie them together when there's a supply voltage (i.e. the car is on) and then sense that if for any reason one of them starts to loose voltage (bad battery, whatever), it shuts off feed to that battery.
- ussually these systems have an override so that when you want to, you can manually set the batteries in parallel (the "BOTH" setting) for winching power or for starting from the backup ("B") battery.
- the only downside compared to the "boat switch" + isolator method is that in most systems you only have the "A" and "BOTH" setting, you have no pure "B" setting... i.e. if your "A" battery actually shorts out, then you will have to physically remove it from the system... you wouldn't want to switch to "BOTH" in that scenario. now if your "A" battery is just low (more typical situation), then you can safely switch to "BOTH" in order to start the car still.
- these manufactures will tell you a solenoid (high current relay) is tried and true simple switch that is less prone to failure than fancy digital switches
- national luna and IBS both offer fancy remote controllers with voltage monitors for both batteries, audible alarms, etc.
- IBS's "BOTH" setting is timer based so you can't easily leave them connected for too long. national luna's "BOTH" setting has a warning light to show you it is engaged.
- IBS's system handles 500 amps (200 continuous) whereas national luna is rated at 400 amps (85 continuous). note the continous rating is very different, might matter for when you want to tie both batteries together for a large winch.
- IBS and National Luna are about the same price, and i hear that Etreme Outback is carrying the IBS system even though their site doesn't show it yet (according to winter overland journal).
4. in intelligently controlled digital switch (hellroaring for example)- pretty much the same as the intelligently controlled solenoid except that the solenoid is replaced my a modern digital switch
- these manufactures will tell you a digital switch is supposedly better technology than a solenoid which can get contacts stuck, worn, corroded, or filmed (opposite of what the solenoid people say, i tend to believe that modern solid state electronics are better than traditional high current relays, but this is personal opinion).
- hellroaring uses the voltage monitoring method of intelligent control instead of just a timer and ignition switch check.. i.e. if you alternator fails then it will sense the non input voltage and isolate your backup battery so that you aren't draining them both. a lesser system might just know that the car was runnign and therefore assume it was safe to tie the batteries together for charge when in reality it would be letting them both run dead.
- hellroaring has a remote switch module that lets you put the system in "A", Automatic, or "BOTH" but doesn not have fancy voltage monitors (you could add these yourself for cheap). it also does not have a timer circuit (so you are more likely to accidentally leave it set to "BOTH" and then potentially run both batteries down).
- hellroaring handles 500 amps (150 continuous)
- hellroaring is a fair bit less expensive than national luna or IBS, but doesn't offer nearly as fancy of controller interface
5. some "i did it this way" method that use pieces from the above types of systems- i guess the ultimate system would be to use 2 digital switches (probably from perfect switch, as they supposedly have the best digital switch) and your own custom microcontroller that would allow you to have all the system sensing and control qualities of national luna/IBS/hellroaring products, but with a "B" setting too (instead of just "A" and "BOTH"). add to that your own digital voltage readouts of both batteries and custom control panel with override switches and timers and audible alarms.
the above would be $$$ and room for errors since it's a custom system instead of a tried and true system tested by thousands of users.
more reading:so what am i going to do?well i'm about a month or so from actually finishing up my battery relocation project and therefore being ready to purchase a system. i'll have to look at my funds when the time comes. i won't do a "boat switch" based system because my batteries are going in my spare tire well in the trunk and i don't want some janky looking giant switch run into the cab, i want a clean remote control.
i'm completely satisfied with what hellroaring offers for the price. i think it's a great system and if funds are tight i'll get it.
if i feel like splurging, i'll get the IBS sytem just for the fancy controls and voltage monitors... it's about the same price as national luna and offers more current handling and timer based "BOTH" setting, and if indeed extreme outback is willing to carry it, then it must be a good product.
please add to this if any of my facts are incorrect, otherwise most things are just my opinion... your mileage my vary.
