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Battery drain in 1994 Chevy Cheyenne 2500

Hi, I’m not a new user, just hadn’t posted in a long time so I had to rejoin. I bought a 94 Chevy 2500 about 1 1/2 months ago because my wife and I were looking for a camper. The truck has an electric lift on the back which is pretty useless to me as it’s in the way of any hitch I put on. I have a friend who has his own shop and he wants the lift for his truck so I told him I’d trade him the lift for a bumper and a tailgate. The truck had been sitting at his shop for 3 weeks and I was more than a little peeved that he hadn’t gotten to it yet so I went and got it yesterday and the battery was stone dead. He said the diodes in the alternator may be going bad but after we got it running, I took it and had it tested and the alternator and battery tested ok. The battery is new because about 2 days after I got the truck the battery was dead too. I figured old truck, old battery so I didn’t even think about it but now I’m wondering if that battery was good. Is it possible for the normal drain from the radio and clock to drain a new battery in 3 weeks? I wouldn’t think so, but I’m hoping so since otherwise I’ve got an issue. My first instict was that lift because it’s connected straight to the battery so I did disconnect it. Thanks.

Was the new battery fully charged at the beginning of the 3 weeks?
It takes up to 8 hours to fully charge a battery. 30 minutes at high current won’t do it.

This calls for an ammeter to actually measure the drain when the vehicle is off. Should be less than 100 milliamps.
If it’s more than 200mA or pulses of higher current there’s definitely a problem.
Pull fuses one by one until the current drops.

I never put a charger on it after I bought it. I did drive the truck several times before I had taken it to his shop. I have to disconnect the negative cable and put the ammeter in between the cable and battery, correct. I appreciate the response. I’m fairly mechanical and there’s not too much I can’t tackle, but like most, I hate diagnosing electrical problems.

I have to disconnect the negative cable and put the ammeter in between the cable and battery

That’s right.

I hate diagnosing electrical problems.

It’s one of my favorite tasks. Thus my “handle”.

Ah, glutton for punishment! lol Glad there are guys like you out there. I do have one more question. This truck is a beater for sure. It runs well and has a big beefy transmission with granny gear but it does have some issues. The panel that covers the fuses in the cab is missing so have no diagram of what’s what. Is there somewhere I can find that without spending 20 bucks on a manual? I’ve done some searching and can’t find anything specific. Thanks.