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<blockquote data-quote="helotaxi" data-source="post: 1583411" data-attributes="member: 550915">That is where an isolator comes in.&nbsp; The two batteries will interact.&nbsp; Not a huge deal with the car running, but as soon as the car is turned off they will attempt to equalize each other.&nbsp; If there is even the slightest difference between the voltage on the two batteries or their ISR, they will go back and forth with each other and one or the other will usually end up dead.If you plan on running two different batteries and don&#039;t want to end up with one or both of them dead sooner than they should be, get an isolator.&nbsp; An isolator is better for this than a solenoid because it isolates the batteries from each other with the car on or off.&nbsp; No interaction.&nbsp; The stereo will only tap into one of the batteries when it needs current (protecting your starting battery from being drained and damaged) and still allows the alt to charge both batteries.&nbsp; A solenoid will do the job with the car off but not with it on.&nbsp; As far as voltage drop goes, you will only lose the voltage once (.7V assuming a standard silicon diode, only .3V for Germanium or Schotky diodes) because each battery has its own diode and they are wired in parallel.&nbsp; Only one diode on each lobe of the parallel circuit so you only have the loss once.&nbsp; If you are really worried about it and are running an unregulated amp in competition and need that extra .3-.7V get a hot alternator (more than 14.4V) to account for the drop.&nbsp; If you are competing this is really all moot though since you are probably running a huge battery bank and they are all the same.&nbsp; If you aren&#039;t competing it won&#039;t matter.</blockquote>

[QUOTE="helotaxi, post: 1583411, member: 550915"] That is where an isolator comes in. The two batteries will interact. Not a huge deal with the car running, but as soon as the car is turned off they will attempt to equalize each other. If there is even the slightest difference between the voltage on the two batteries or their ISR, they will go back and forth with each other and one or the other will usually end up dead. If you plan on running two different batteries and don't want to end up with one or both of them dead sooner than they should be, get an isolator. An isolator is better for this than a solenoid because it isolates the batteries from each other with the car on or off. No interaction. The stereo will only tap into one of the batteries when it needs current (protecting your starting battery from being drained and damaged) and still allows the alt to charge both batteries. A solenoid will do the job with the car off but not with it on. As far as voltage drop goes, you will only lose the voltage once (.7V assuming a standard silicon diode, only .3V for Germanium or Schotky diodes) because each battery has its own diode and they are wired in parallel. Only one diode on each lobe of the parallel circuit so you only have the loss once. If you are really worried about it and are running an unregulated amp in competition and need that extra .3-.7V get a hot alternator (more than 14.4V) to account for the drop. If you are competing this is really all moot though since you are probably running a huge battery bank and they are all the same. If you aren't competing it won't matter. [/QUOTE]

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