Duel Battery Install Considerations and Advice

Preparing for a dual battery install. I've done something similar before in a considerably less expensive van; it always makes me very nervous to mess around with anything electrical. Even though there is already an exhaustive thread on duel batteries I was hoping to start a thread with comments and suggestions on a few specific questions/issues.

Starting out I'll mostly using parts from a previous duel battery set up: a 125 amp VSR connected to an Optima blue top via 4awg wire and Anderson connectors for easy disconnect. Not planning for for emergency jump start capability to avoid having to plan for large starting currents (I'll just keep a jump pack charged).

Questions/ issues:

1) Do 2nd gen Toyota's have "smart" alternators? I'm fairly sure they do not and a regular VSR/diode isolator will be fine.

2) How many amps and what size fuse/VSR should one expect an AGM battery draw when charging and how does running accessories on top of a charging battery effect total amp draw?

Right now the plan is to go with the 125amp VSR I have on hand along with 80amp fuses on the starting and house batteries (with VSR between). It's worked for me in the past where I had a stereo amp and a battery but at the time I only an 80amp alternator where the Tacoma with tow package as 130amp alt.

I've read anywhere from 15amps to 40amp charging draw can be expected, throw a stereo amp (400 watt) and a few lights into the mix and it's getting pretty close to 80amps. I'm assuming accessory amps are added to charging battery amps (ie the amps are not "taken from" the battery and the alternator is only supplying recharging amps to the battery and not the accessories too).

2b) Any suggestions of the type of fuse to connect to the batteries - I have AGU fuse holders on hand but would rather have something right on the battery terminal.


3) I'd like to hear opinions on mixing lead acid (starting) and AGM (house) batteries, I did this for years with not problems (an AGM is just a sealed lead acid battery). I will eventually graduate to the preferred DC to DC charger and solar panels but I'm keeping it cheap for now. Would a DC to DC charger put less strain on the alternator?

3b) When the VSR opens up at ~13v how quickly does the starting battery "dump" voltage into the house battery especially if the house batters is, say, only at 80% charged (or does the starter stay topped up while the alternator feeds the house)?


4) Ideas on battery placement. My 2015 has no room in the engine bay so its either in the access cab or in the bed. I keep changing my mind on this but leaning towards [strike]passenger side in the cab[/strike] truck bed. I plan on making the battery fairly easy to disconnect (using Anderson connectors) and bring inside for full charging / conditioning / float charge maintenance over the winter etc.

Main reason for putting it in the bed is that (1)I would not mind drilling a battery holder in the bed (2) a bit easier to run the wire (4awg) from starter to the bed (3) if the battery blows up or in the event of an accident (4) the heat inside the cab on a hot sunny days may be problematic for an AGM battery.

Reasons for the cab (1)I'll have some accessories (amps, stereo) and a few electronics (cell phone) charging of the house battery and if the battery is in the bed I'll have to wire electric into the cab (2) the starting battery wire won't have to be quite as long.

5) Where to place the ground. I assume the factory grounds by the driver kick panel and below the drivers seat are not ideal for 4awg ground wire from second battery so the question is: is it better to run a ground wire from the start battery or is a chassis ground just as good / better / same diff. For now I plan on using the chassis ground found near the drivers side wheel well.

However, the last time I did a duel battery set up I ran a 4ga wire to the starter battery negative and when I tried to move the ground to the chassis (may have been a seat bolt) the stereo amp picked a wine that changed frequency with engine/alternator rpm. Any opinions on grounding to the start battery (copper is a better conductor then steel) vs a shorter ground wire to the chassis (negative charge does not travel to the negative terminal through the chassis, rather charge "dies" at the ground)?


** I doubt I'll ever get a wench installed but if I do I assume it's best to be powered but the starter battery and only used when the engine is running correct? **


6) How to attach the VSR close to the starter battery - my first thought is to screw the VSR into the body someplace under the hood in but I don't want to create a spot for rust to start. How to screw stuff into painted steel without creating a rust spot? Seal with RTV? Or maybe I should just use 3M tape or even RTV to "glue" the VSR near the battery?


7) How to run the wires in general and keep everything water proof (e.g. blue sea clam sell). If I go with battery in the cab I'd plan on running 4ga wire through the driver side firewall grommet where a bunch of other wires are passing through, how much care needs to be taken to reseal the grommet - the factory wires are sealed up pretty good - I don't go swimming but I definitely splash around a bit.


8) [bonus] I'd like to hear how solar charging is working out and how folks are running the panel wires and attaching the panels, my impression is that 200w - 300w is required to keep a 100ah battery charged. Given the expense this is a down the road option for me. Also be curious about "shore power" options that's WAY down the road for me as I'm mostly interested in boondocking.


*** Are there any deities to appease or rituals to perform which will decrease the likely hood of mistakes as I and others contemplate this relatively straightforward but potentially disastrous operation? ****


Any suggestions/clarifications on any of these points greatly appreciated. Thanks!