Battery drain, read the FAQs
 

Working with the dual battery system in my 99 diesel Suburban ex-fire truck. I’ve had a battery drain that I chocked up to a parasitic draw but now not so sure.

I’ve charged the batteries in the truck to full with a trickle charger (connected w an in-series cable that’s OEM) while the batteries are isolated from the system w use of quick disconnects affixed to the negative terminals. A week after sitting the charge isn’t enough to crank the engine sufficiently despite the use of the disconnectors and no apparent power to the system.

Therefore I’m suspicious that one of the batteries isn’t holding a charge. I’ll remove these and have them tested (dated 11/20 generic Fleet Farm brand).

Any chance that despite the use of these disconnects and no apparent power to the truck a parasitic draw could still occur?

..

Re: Battery drain, read the FAQs
 

Pete, I would say it’s incredibly unlikely it’s parasitic if you’ve got the batteries isolated from the system. You’ve probably got a bad cell. Have you tried checking the voltage on the individual batteries to see if one is weaker than the other?

Seems batteries these days are pretty hit and miss, we are a dealer for interstate at work and I can tell you they are a mixed bag as far as longevity goes. Some will last several years some a few months.

I will say I’ve been pretty impressed with the OEM battery in my 2018 Sierra 2500. 110,000 and it has never skipped a beat since day 1.

Re: Battery drain, read the FAQs
 

Thanks buddy. Dumb question, do I dial the meter to this location then check the volts across the terminals?

Re: Battery drain, read the FAQs
 

The DCV 20 range should be suitable.

On your disconnects do you have a bypass wire on either one of them to keep radio memory?

Re: Battery drain, read the FAQs
 

Thanks. I’ve got 12.55 on one side and 12.65 on the other. I had these on a trickle charger this week. I’ll check the volts after a few days and see if one or both drain down.

I don’t have a bypass wire. The clock on the radio goes dead when I loosen the knobs on the bypasses.

Re: Battery drain, read the FAQs
 

Pretty interesting. 12.6 volts is normally considered a fully charged battery. I’d keep an eye on them over the next few days and see if they fall off at all. Keep in mind it’s not out of the question to have a battery pass the voltage test but be damaged and not able to kick the Amps out necessary to fire it off. I think I’d have them load tested and NAPA or similar next.

Re: Battery drain, read the FAQs
 

Tonight the meter gave similar readings. Not enough juice to start the engine though. Headlights were bright.

I swapped in two Delco 78 series batteries that had voltage readings of 12.3 and 12.7. These fired the engine right up.

Two batteries sure doubles the hassle. Tyler, I’ll lug the original ones to have the cranking amps checked. Suspect one is bad. Meanwhile, I’ll keep the Delco’s in place and see if those get drained by chance.

Thanks and stay tuned. BTW why two batteries w a diesel? Compression so high the starter needs more oommpf?

Re: Battery drain, read the FAQs
 

Good deal Pete, I bet like you said one of those batteries is no bueno.

Re: Battery drain, read the FAQs
 

Oommpf must be the new millennial word for amps.. :) Batteries in series -- voltage adds, available current remains the same... Batteries in parallel -- current adds, available voltage remains the same..

Re: Battery drain, read the FAQs
 

Lol! Thanks guys. I got an A in both physics classes but those were a long time ago. I’ll try cranking it over this weekend.

Re: Battery drain, read the FAQs
 

BOTH batteries failed an amp test. Each has a manufacture date of 11/20 :(

Have two 78 series Delco replacements en route.

Re: Battery drain, read the FAQs
 

I had a feeling that would be the case, seems like batteries can be a real crap shoot these days. Glad you got it figured out.