[gagala]

I guess my question will show you that I know nothing about this...

Here is what I read in some other forum :

" It is very important to use 2 batteries of same capacity as using a larger battery would cause premature battery death in the smaller battery. Reason being, they have different internal resistance and the larger battery will always be trying to charge the smaller battery. "

Any truth to this?

My reasoning is that if I have in isolator between the two, the alternator will provide the current to both batteries when running and when not running, the batteries will be isolated .

Is there something I do not understand?

 

[skorp1702]

I guess my question will show you that I know nothing about this...

Here is what I read in some other forum :

" It is very important to use 2 batteries of same capacity as using a larger battery would cause premature battery death in the smaller battery. Reason being, they have different internal resistance and the larger battery will always be trying to charge the smaller battery. "

Any truth to this?

My reasoning is that if I have in isolator between the two, the alternator will provide the current to both batteries when running and when not running, the batteries will be isolated .

Is there something I do not understand?

they need to be similar but don't have to be exact. iv had multiple batteries in vehicles for sound systems for years with no isolation at all between them. id try to keep it within 200 amps.
my past battery setup was a 1000 amp main battery and 3- 800 amps aux batteries for the system. the batteries will take what they need and that's it unless you have a bad altenator or just a faulty battery cell

 

[Dick]

Someone correct me if I am wrong but I didn't think the size mattered much using a solenoid type isolator as long as they were the same type battery.

I always thought it was most important not to undersize the house battery (second battery) because batteries do not like to be discharged more than 50% and in our case we could be running a small battery dead quickly. A battery will only take so many deep discharge cycles and a marine (deep cycle battery) will take twice as many as a regular battery and all batteries should be charged back up within a day. To me this will be the biggest killers of our house batteries.

Also we should make sure to properly size the wire connecting the batteries to the isolator solenoid, undersizing these wires can be harmful to the batteries. Also make sure the ignition wire is connected to true ignition source.

What type of isolator is everyone here using? Anyone using a diode type? I steered away from the diode type because the voltage drop could cause the battery to not fully charge and decrease the life span.

Here is video if anyone here does not understand what we are talking about.
Battery Isolators - Types & How to Install | Car Audio 101 - YouTube

 

[gagala]

Thanks guys. It makes it a bit clearer.

 

[skorp1702]

are yall using the motor home type isolaters . where the batteries are separated but can be charged when motor is running. i plan on using a 300 amp solenoid electric switch manual connection with a toggle. keep it simple.

 

[Dick]

Don't know if that would work for me Skorp, I have a good memory its just not very long!

 

[The Wire]

The biggest issue you have with mismatched batteries is when they are sitting connected while the vehicle is off. Any current flow as the batteries try to equalize their voltages, will drain the batteries. This is not nearly as much of an issue when the alternator is on and charging. Both batteries see a voltage above their nominal voltage and both take on a charge.

A solenoid battery isolator can stop the current leaks by disconnecting the batteries from each other when the engine is off. And it doesn't have a voltage drop like a diode isolator. 0.7 volts doesn't sound like much, but its the full range of charge on a lead acid battery. I would wire the solenoid from a source that's switched with the ignition and put a toggle switch in series. That way you can keep the second battery isolated if you want while the engine is on but you can't forget the solenoid on because it goes off when you shut the key off.

 

[Dick]

Well put sir! You should speak up more often, you explain things very well!

 

[skorp1702]

Don't know if that would work for me Skorp, I have a good memory its just not very long!

lol well my plans were to take the second battery and have all the aftermarket accessories. so when my switch is off the machine battery is only connected to the machine and the second battery can still run my accessories till the battery runs out or i flip the switch and begin its charge.

this will work great at my lease when the kiddos are swimming and adults bs ing. listen to music till the radio dies crank the pioneer and flip the switch and recharge the secondary battery