Second battery voltage question

[javiecholson188]

Hey folks.

I’ve just got done installing a second battery + wiring in the Jeep. I was trying to research this before buying the gear but couldn’t get a definite answer so I figured I’d just rig it up and look for any problems.

The setup I’m using is just the kit from 4wdsupacentre which is basically a VSR that cuts in when the main batt is charged over a certain voltage. According to the indicator led on the VSR it is sending charge to the backup batt, however when I check it with my multimeter, the backup batt is only reading 12.85v with the engine running.. My understanding is when the charging is actually running it should be reading somewhere around the 14 mark. Do I just need to charge it a bit longer? Or should it be reading higher while the engine is running?

Do JKs have one of the shitty alternators they warned me about that don’t generate enough juice to charge 2 batteries?

Edit: I chucked the multi on the main battery and it’s reading 14.x volt so it’s at full pretty much.

[Barboots]

Gotta ask... the VSR is installed the right way around? Apologies for the but it happens [emoji2]

Put your meter across the input and output of the VSR... this checks it for voltage drop.

If no significant voltage present there, repeat using the same test method from:
- the main battery to the input of the VSR;
- the output of the VSR to the second battery.

Record all readings and report back. Them volts are hiding somewhere.

[st_za]

Are you using the under-bonnet 2nd battery tray or is the battery in the back?
What size and length cabling are you using?
Do you have any fuses or circuit breakers wired in?
What type and size of battery are you using?

The JK doesn't have a smart voltage-regulating alternator but it isn't a completely "dumb" system either (there are other threads that go into more detail around this).

[mick666]

once your 2nd battery is connected to the first via the VSR your voltsge readings should be the same. Check your grounding between the main battery and the chassis, and the body. Check the aux battery the same. check between body and chassis. all readings should be near 0 ohms. for instance if your 2nd battery is earthed to the chassis and the main battery has a good ground to the body but poor to the chassis, u will get the issues you are seeing. I have had this issue...