MEP-803A

[sigley89]

I’m having issues with a battery drain. I fully charged both of my batteries to 13v and they balanced around 12.3 or so. Did a monthly start and ran for an hour. Shut the set down and I left the batteries connected up with and the dead crank switch to off. Came back 8 days later and one battery (left side, starter side) was dead, it read .3v. The other was still charged at 12.2. I replaced the battery that drained with a known good battery and repeat. Same issue. Even when I charge them both up and I attempt to start it both of my batteries drop to 6v then to 4v while holding the master start switch. Are my batteries not big enough or is there another problem I should be looking for?

 

[glcaines]

The MEP803A is supposed to have 800U batteries installed with 800 CCA at 0 deg. F. and 1000 CA at 32 deg. F. Normally, the genset doesn't require batteries that large, but you do live in Alaska. I've seen a lot of Optima Red Tops in those generators. It also sounds suspicious to me that only one battery is draining. You should never replace just one battery. Batteries hooked up in series for 24VDC should be purchased in pairs or one battery is very likely to fail prematurely.

 

[sigley89]

This is the batteries I have now. It’s 76 degrees right now so CCA isn’t an issue right now. The one in the picture is the battery that’s dying.

 

[Light in the Dark]

If BOTH batteries voltage is taking a dive upon start, you need to replace them both. The one that is showing the 12-13V when sitting idle may have only a surface charge, but no amperage upon use.

Battery quality has not improved since covid...

 

[Guyfang]

This is the batteries I have now. It’s 76 degrees right now so CCA isn’t an issue right now. The one in the picture is the battery that’s dying. View attachment 869320

Take both batteries out. Charge them. Then load test them. If you don't have the load tester, go to someone who has it. Its the ONLY way to KNOW if the battery is good.

Oh, looking at your picture. You need to push the battery terminal down until the post is even with the top of the clamp. When its real cold, and you are trying to start, the draw from the starter has been known to burn off the top of the battery post. When its up too high, you do not have as much surface area, to pass the current safely. Recasting battery terminals is an art.

 

[zarathustra]

If one battery is discharging and not both I'd replace the batteries. It is false economy to replace only one battery with the two in series.

I have three 802/3 gens and have installed battery isolator switches on the ground side of the battery (battery on the left, fuel pump side).

I do this with my jeeps and electric start mowers as well.

They can sit for months and the batts hold their charge.

You could also, although I've never tried it, pull out the circuit breaker in the control box.

 

[Ray70]

It sounds to me like both batteries were actually discharged, but one was still showing a 12.2v surface charge.
Napa Legend are excellent batteries and yours are not very old ( still under warranty )
I would start with Guy's suggestion to remove and fully charge both batteries, then load test, or have them load tested at NAPA.
if they are good I would begin by checking for a parasitic drain on you batteries. First place I would look is the alternator's internal diodes.
I don't recall off hand if the dead crank switch being off disconnects the alternator feed or not.
If it does not, your batteries could be draining out through the alternator.

 

[Guyfang]

S10 will not change anything.

 

[kloppk]

The Dead Crank switch does not disconnect the alternator. The alternator is always connected to the batteries unless you disconnect the batterry cables.

 

[sigley89]

It sounds to me like both batteries were actually discharged, but one was still showing a 12.2v surface charge.
Napa Legend are excellent batteries and yours are not very old ( still under warranty )
I would start with Guy's suggestion to remove and fully charge both batteries, then load test, or have them load tested at NAPA.
if they are good I would begin by checking for a parasitic drain on you batteries. First place I would look is the alternator's internal diodes.
I don't recall off hand if the dead crank switch being off disconnects the alternator feed or not.
If it does not, your batteries could be draining out through the alternator.

Would you be willing to walk me through looking for a drain on the alternator? I bought 2 optima redtop batteries and they were doing fine for about 2 weeks holding at around 24v total then today went to start it and the starter clicked and wouldn't turn over. Checked both batteries and they were at 9.2v each. Ive been using the generator every 1-2 days for about 4-8hrs

 

[Ray70]

Absolutely.
One way is to disconnect the charging output wires from the back of the alternator, these are the 2 wires on the larger stud with a + cast into the alternator housing. Usually on the bottom or bottom left depending on how your alternator is clocked.
Check using your volt meter, you should have 24V+ on the wires.
With the wires off the stud, set up your meter to test DC amps. put the positive lead on one of the wires or any other 24V + source ( such as the heavy wires on the back of the starter solenoid ) and put the negative lead on the + stud of the alternator.
Any current flow will indicate a bad diode in the alternator.

 

[Ray70]

another way is to simply put a DC light bulb ( 12 or 24V will work ) between the disconnected wires and alternator stud.
If the bulb glows you have a battery draw caused by a bad alternator diode.

 

[Guyfang]

another way is to simply put a DC light bulb ( 12 or 24V will work ) between the disconnected wires and alternator stud.
If the bulb glows you have a battery draw caused by a bad alternator diode.

This is about the most underrated test equipment in the history of man. Back in the day, that's all we had, and it works great. Simple, easy and handy. Any fool can make one. My first was a dash light socket from a M-35 truck. one lead was 6 feet of wire attached to one lead on the socket, with a roach clip on it. The other lead was an old Multi Meter lead hooked to the socket. Clip the roach clip to ground, and the M.M. lead would be held on any place you wanted to check for 24 volts. When I was done, I wound the long lead around the M.M. lead and stuck it in my back pocket. There are a million such tools to be had, and all cost way more then my simple one. Just get one.

 

[Farmitall]

This is about the most underrated test equipment in the history of man. Back in the day, that's all we had, and it works great. Simple, easy and handy. Any fool can make one. My first was a dash light socket from a M-35 truck. one lead was 6 feet of wire attached to one lead on the socket, with a roach clip on it. The other lead was an old Multi Meter lead hooked to the socket. Clip the roach clip to ground, and the M.M. lead would be held on any place you wanted to check for 24 volts. When I was done, I wound the long lead around the M.M. lead and stuck it in my back pocket. There are a million such tools to be had, and all cost way more then my simple one. Just get one.

Agree, a most useful tool.

I keep a half dozen of them on hand all the time. One in each toolbox, one on the tractor, one in the truck.