Dead battery

[Huckleberry]

I have a 1978 K 15. The truck has 2 batteries. The passenger side battery ( starter battery) went dead last week. I replaced it with a new battery, it was 7 years old. The truck sat for 3 days and the new battery is dead????. I didn't see any fluctuations in the volt meter or any missing in the motor when driving. I have an after market horn attached to the battery. Need help troubleshooting. Thanks

 

[Scott91370]

Always replace batteries in pairs. It is not uncommon for a bad battery to ruin a good battery depending on how they are connected.

 

[Huckleberry]

Thanks

 

[Grit dog]

It’s pretty unlikely that a K15 came with a factory dual battery setup. Maybe no chance. And equally unlikely that any of us would know how both batteries are wired up, what they’re powering and how they are combined or separated. And what may or may not be hooked to either battery and whether all those components are functioning properly and/or don’t have parasitic draw.
So that said, one of the most likely causes of the new battery draining is that it’s trying to equalize with the 2nd battery. Although it sounds like there was no issue with battery draw down until just last week.
I’d start by making sure the 2nd battery is out of the picture. Then see how it does.
May require an amp meter to verify how much draw is coming off the primary battery and then start chasing down the load it’s supplying.

Sorry for the non - answer but imo there’s not really a concise “check this it’s usually the problem” type of answer.

 

[fast 99]

Check for a draw. An easy although not foolproof way is with a test light. Put in series with battery cable, turn off or disconnect any aftermarket equipment such as alarm, radio or amp. Isolate second battery. If it lights further diagnosis is needed.

Agree with previous posters, batteries should be replaced in pairs. Second battery could be bad causing new battery to fail. Also check alternator, output should be around 14V.

 

[Ricko1966]

I can't count how many batteries I've seen replaced that the real problem was the alternator less common is draw. But a dead battery everyone just sticks in a new battery without checking anything first.

 

[sidschev]

was this a diesel truck before or is it still. daul batts might have been a plow truck too....anutter reason for daul batts....agree with others isolate the second batt then do draw test......

 

[sidschev]

I can't count how many batteries I've seen replaced that the real problem was the alternator less common is draw. But a dead battery everyone just sticks in a new battery without checking anything first.

i had a brand new car batt died (ie wont start ) put in a new bat fired right up ,ONE year later exactly the car no start , had full voltage in batt. still car no start. turned out the batt was bad again. it was one of them new fangled batteries and with those batts one volt that is dead in those batts will not start the car. That was on a 2017 Kia sorento and also a 2012 dodge dart both of those cars had the same type battery cant remember what batts they were.

 

[armor2111]

I keep thinking is there a battery isolator? I had my alternator replaced with a 110 amp and a new battery.

 

[Ricko1966]

I keep thinking is there a battery isolator? I had my alternator replaced with a 110 amp and a new battery.

I'm thinking he has an isolator and a draw which I stated on his other thread about this. P.S. when I run dual batteries with an isolator I've never changed both batteries at the same time and never had a problem, especially when you figure the batteries will discharge and charge at different rates and a majority of the time they aren't even connected to each other. JMHO.

 

[75gmck25]

When you find dual batteries in a gasoline squarebody, it’s because they have the camper special package, maybe trailer towing package, or have added a plow or winch. The main battery and the aux battery then have totally different uses, so they are seldom identical.

 

[Huckleberry]

Thanks. Appreciate you all. Learning every day

 

[Keith Seymore]

When you find dual batteries in a gasoline squarebody, it’s because they have the camper special package, maybe trailer towing package, or have added a plow or winch. The main battery and the aux battery then have totally different uses, so they are seldom identical.

This.

RPO TP2 was the spare battery on gas jobs (pickup only). It was an auxiliary battery for campers and trailers and was therefore wired differently than the dual battery setup on diesel.

TP2 was not available on Suburban, but there was an SEO setup for Suburban (that would be super rare).

K

 

[Grit dog]

i had a brand new car batt died (ie wont start ) put in a new bat fired right up ,ONE year later exactly the car no start , had full voltage in batt. still car no start. turned out the batt was bad again. it was one of them new fangled batteries and with those batts one volt that is dead in those batts will not start the car. That was on a 2017 Kia sorento and also a 2012 dodge dart both of those cars had the same type battery cant remember what batts they were.

AGM?
Can’t say I’ve ever seen a battery show 12V and be dead. Not a fla sla agm or lifepo4.
If you meant 1 dead cell, yeah that’s 2+ volts down and could be a dead short in the battery. I’d expect that to not work.