Why is my alternator not charging my second batt??

[hispls 5,000+ posts]

Sounded like a bad connection or blown fuse to me. I suspect you'll start popping those 80A fuses though. #4 cable is a bit inadequate, but I've got away with that much power depending on listening habits. I'd have that second battery load tested (pull it out and take it into a parts store).

 

[oldschool4me 10+ year member]

25' 1/0 WELDING CABLE EXCELENE RED MADE IN USA | eBay

thats the wire i used. i bought 100ft of it a couple years back. has gone up in price a bit but its flexibility is pretty good and he sells it in black and red. my buddy bought some black and we traded some so we could have each color for our installs. nice wire.

 

[Tom760t]

Hi

if your cables are not big enough there will be significant voltage drop across it when your system is drawing current you need to put a multimeter from the '+' on your alternator to the '+' on your rear battery with the system going fairly hard or even better if you can put a continuous load on the rear battery while testing.

if there is voltage drop it will show on the meter. e.g. 01.25v this means the rear battery would see 1.25v less than the alternator. e.g. alt charging at 14.25v the rear battery would only be reaching 13.00v, and this will not charge it fully.

if there is minimal voltage drop on the '+' side, do the same for the '-'. one lead of the meter onto the front battery negative and the other on your rear battery negative.

Tom.

 

[SunnykhangHCCA 10+ year member]

Sounds like u don't have a distribution Block after your second battery. Then two 4 awg out to your 2 amps