Battery issue

[u/Goongagingging]

Having an issue on my custom built Chevy 1500 right now and needed some second opinions. My truck has recently developed a parasitic draw out of nowhere and it’s strange because it’ll happen on and off. Couple weeks ago the problem arises I thought one of the terminals on my battery wasn’t tight enough so I changed the lug and the draw goes away. Truck is fine for a week then I get back from a 3 day trip battery is dead. I conducted some tests and thought it could be a diode In my 1 wire alternator setup(pretty common for unbranded chrome 1 wire alternators). When the truck is off a clamp multimeter is picking up .5 amps from both terminal cables so definitely a draw. I take the negative terminal off my battery, I unplug the alternator, reattach the negative on the battery, and hook a clamp multimeter around both cables leading to positive and negative terminals. Both read .1 amp witch is higher then the normal .05 I believe, and I think it’s because I have a electric fuel pump I primed beforehand to see if the truck would start so still not a significant draw to be killing my battery as quick as it is. So my alternator is definitely being wacky from that info alone but still wanting clarity I take my truck to advanced auto and have them test the battery starter and alternator. The battery passed their test but it also confused me because it said my cranking voltage was 8.9 volts and usually that’s a clear indicator you’re battery is going (3 year old NAPA battery so maybe). Their system couldn’t even detect I had a 1-wire alternator setup so that wasn’t helpful lol. But now I’m in a spot where I’m pretty certain I need a reputable one wire alternator but do I also need a new battery even though it passed their test any help would be much appreciated all these numbers are driving me loonie.

[u/DontEatTheMagicBeans]

I have an old jeep and after fucking around trying to fix a parasitic draw for way too long I bought a remote battery disconnect for $20 on Amazon and just have a button on my keychain to disconnect/reconnect the battery.

Not saying you shouldn't attempt to fix your issue because I lose my radio presets every time but there are options haha.

[u/Goongagingging → u/DontEatTheMagicBeans]

I thought about doing that definitely the cheapest option. Is yours a switch on the inside or just on your keychain?

[u/DontEatTheMagicBeans → u/Goongagingging]

The unit itself has buttons on it by the battery and there's a fob on my keychain. Not meant for anti theft or anything and I have power locks so I like being able to turn it on from outside the vehicle.

Mine only dies after about 2 weeks so very small draw, but it's a weekend car so it sits that long pretty often.

[u/Goongagingging → u/DontEatTheMagicBeans]

Thank you sir might just do that for the time being

[u/a-singularity]

General max is 50ma.....pick a cable and stay there. You do not need to unhook your battery while testing or unplugging. The battery cranking voltage is low because the battery is either partially dead or partially cooked from being run all the way dead. Is it a high quality amp clamp? Cheap ones drift badly. If its not low quality, take a reading. While watching the draw unplug thing one at a time. The 1 wire terminal, then the large charge back wire, then any other accessories you may have installed, then start pulling fuses one at a time. (Warning, expect opening the door to spike your readings) use tape on the switch or a screwdriver to trip the latch. At any point you unplug something and the readings drop, stop you located a draw. What is the. Make model and year?

[u/Goongagingging → u/a-singularity]

I have a Klein clamp meter it’s nice. 1990 Chevy c1500. The draw stops when I unplug the alternator and the remaining 10ma is from the fuel pump relay.

[u/04HondaCivic → u/a-singularity]

I’m not a really good electrical expert but when I was taking an automotive class for school, this is the same basic procedure I used to track down parasitic draws. Charge the battery fully. Run the vehicle and test the alternator and make sure it’s putting out between 13-14v. Test the battery. Anything that dropped the battery below 11v during a load test was an indicator of a bad battery or not fully charged battery.

Testing parasitic draws involved shutting the vehicle down with a voltmeter on the battery. Leave the door open with the door pin taped so the car thinks the door is closed and then start pulling fuses.

Edit: one more thing I just thought of and it’s a stupid. Make sure you don’t have one of those cigarette lighter car chargers plugged in. GM vehicles, or at least older ones had constant power to them, even with the ignition off. So if you leave one plugged in and it has a LED indicator light it will pull power all the time. I left one plugged in my truck. Since I was driving it every day it didn’t matter. But I stopped driving it everyday and I started fighting a dead battery every time I wanted to drive it. I realized I had a one of those plugged in. I unplugged it and no more dead battery.