Sometimes battery dead

Most of the time, my '85 K5 Blazer with 6.2L diesel starts just fine. A little slow and rough on cold mornings, but most of the time it is fine. But it seems that the last 3-4 months, if I say for instance drove my truck on
Friday for a few errands, and then didn't try to crank it over again until late Sunday or Monday morning, then the battery is dead for some reason. The starter clicks and all, but I have to throw the charger on it for about 15-25 minutes and then she starts. Not sure why this is happening. There is nothing left on that I know of. It does have power windows and locks and is parked on an incline in the driveway. Also has 2 amps for my stereo but they are hooked up with a remote wire so they shouldn't be staying on. But again, if I drive it daily, it always starts fine, this is just when I haven't driven it for a couple of days! So does anyone here have any ideas at all? Would really appreciate it. Thanks much.
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Hello Mark,
Check for parasitic loads on your batteries when engine is off. Clean the terminals and cable connections. Clean the ground cable connections to the engine block. Have your alternator output tested. Have your batteries load tested.
Good luck and let us know how things go.
Franko

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What are parasitic loads and how do you check for them? The battery terminals have recently been cleaned and sprayed with some of that battery corrosion stuff. Any other ideas?

on
until
all?
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Hello Mark,
Make sure engine is off, ignition is off. Disconnect the positive battery cable from the battery. Use a multi-meter on "Amp"/current mode between the positive battery cable and positive battery terminal to measure how much current is flowing (start at HIGHEST setting on multimeter, work your way down if needed to get more accurate readings).
How old is the starter? Starter connections clean, too?
Franko

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