MEP-8xx Battery Information

MEP-8xx batteries

MEP-802A 5kw generator
The military is currently using Optima Yelloptop 51R batteries x 2 in series for the 24 volt system

MEP-803A 10kw generator
The military is currently using Optima Redtop 34/78 batteries x 2 in series for the 24 volt system

Optima batteries are AGM. (Absorbent Glass Mat) A AGM type charger is the preferred method to get the most out of the batteries. The Optima batteries being found in most vehicles and generators might look like they are dead. Give them some love. Take them out and use a AGM type battery charger for a few days. You will be surprised when they come back to life. Some generators and vehicles might also have a pulse solar charger on them. The solar charger is really meant to keep the batteries at their best after they are fully charged. The best method would to fully charge your batteries, and then let the pulse solar charger maintain them.

Military vehicles and generator use a 24 volt base electrical system. The NATO standard is single pin 24v slave receptacle.

Charging thru slave port thread

I know this might sound odd but for the 802 I use a pair of lawn mower batteries. They are cost effective and work great.

To keep from cutting the factory cables I just buy 3 pre-made battery cables and replace the factory cables. Going this route a set of batteries and cables are about $80.

AGM = Abpsorbed Glass Mat

It's a non-spillable lead acid, they put only enough electrolyte in there to saturate a paste, there's no free flowing fluid.

As for Optimas, I'm not a fan anymore. They changed their production a few years back and the quality bottomed out. I've had several fail open all of a sudden in the middle of nowhere - not the best way to get a warm fuzzy feeling about them IMHO...

Howdy,
If I get in a new Optima battery. I put the battery thru some paces before its installed. I will ensure the battery charges, on a AGM specific charger. I will load test the battery. re-charge. I will then draw the battery down with a AC converter, re-charge, let sit 24 hours and take voltage reading. Load test the battery some more to ensure it hold a load, and draw it down and then re-charge the battery. I will do this for both batteries to be installed. Lately I have been checking new pairs of Optima Yellowtop D51R batteries.

Howdy,

All the optima batteries which I have purchased have been working good so far. I just make sure I abuse them a little in the first week discharging and then re-charging them a few times to make sure I can rely on them.

I've had a Red top Optima that's been in my Jeep for 18 years! still works! That being said I got one for my truck a few years ago and it only lasted 3 years. They don't seam to be the same quality anymore and a $234 each vs $105 for a Mega-tron II it was a no brainer for me. As for MEP-803A Battery size I wanted ones that would: Fit the stock battery plastic boxes, work with the factory tie downs, and also have terminals away from the tie downs and engine block and closer to the door. Interstate MT-47/H5-1 works great. Others will fit but these are about perfect.

Howdy,
MEP-802A 5kw generator
the fitment is Group 51R batteries x 2 in series for the 24 volt system

MEP-803A 10kw generator
the fitment is a Group 34, or a 34/78 batteries x 2 in series for the 24 volt system

Whatever battery manufacturer you like.

MEP-802A MEP-803A battery hold downs

Thanks for all the battery info guys!

Can anyone verify that there is NOT an extra 1.7" of room in the battery compartment/tray for a Group 35/85 battery? Specs of L, W, H for 35/85 are 9.1L, 6.9W, 8.9H versus the Group 51R sizing of 9.4L, 5.1W, 8.8H.

It seems there are some very capable batteries at much more affordable prices than the Group 51R.... if the 35/85 would fit without substantial modification.

Thank you.

I'm using lawn mower batteries as well.

lonesouth said:

I'm using lawn mower batteries as well.

Click to expand...

I'm back to using those too, after BOTH my Optima yellow-tops flat-out DIED after I let the genset sit without starting for about six weeks.

Six weeks. They were reading NEGATIVE loads.

I've since connected a VOM and DC ammeter and can't find ANY ghost drain, zero, zip, nada.

Bad news is, what cost me $154 each about 18 months ago are now closer to $250. Good news is, Amazon refunded my money.

So they're sitting here on trickle chargers, and one won't hold any charge, the other won't go about 10v. I have a 10 amp charger I hooked up for a while, didn't help. Carbon pile testing halved the available voltage once one of them got to 11V and won't go over 9 now, which disappears all on its own in about a week, back to zero.

I just put the original lawn/garden tractor batteries the seller had in them back in. They'd been on pulse-chargers for about a year, used for some other things (like jump starting my HMMWV when an Optima went tatas-up this past winter - again refunded, but bought another new as I still had ONE), work great. So I have a pulsetech charger on the genset now, batteries are fully charged after a couple weeks.

Think I'll run it tomorrow, but I'm no longer an Optima fan-boi.

Pays your money and takes your chances.

A pair of $33 batterys isnt looking half bad now? Yikes i wont even spend $140 on any car battery. Would rather keep two junkers on charge and tote a set of jumper cables around.

The biggest issue I've had with the lawn batteries is most of them today are crap. They have internal discharge issues and if you don't keep a trickle charger on them they will die and sulfate.

I find that at least half of the batteries I buy have self discharge issues.

The lawn batteries have enough juice to start a MEP when they are fresh and hot. BUT if they are not pretty much topped up their CCA drops off dramatically. If you have one battery with the self discharge issue and it sits more than a month without running the generator may not start.

That is what I have been seeing at least.

If anyone wants to go that route I recommend buying a pair, top them up with a charger then set them aside for 1-2 months. If they have lost more than a couple tenths of a volt they are likely junk and will fail on you when you need them.

Just updating; my local O'Reilly Auto has 51R batteries in stock. Two flavors; standard and premium. Standard = 450CCA and Premium = 500CCA. 2-yr warranty on both. $129 and $154 respectively. Certainly not making any claims about their performance, just offering that there are some alternatives out there.

I put a 5 watt pulsetech charger on the lead-acid tractor batteries I put back into my genset. Measured 24.4V. Let it sit for about two weeks - solar panel gets maybe 4-5 hours full sun a day, that much at angles/indirect. Batteries measured 24.4. Ran set at 80-rated load for about an hour, batteries at 25.4V. I'll check again in a month. Keeping fingers crossed. Meanwhile, friend has an Optima battery refresher/charger setup, he thinks we can bring the other ones back to life.

Used to pick up Exide classic 51R @ TSC for $89/ea without core (my local store never asked for cores, so it was a great deal). They don't seem to carry them anymore, but now have Traveller brand T-51R @ $99 without core. YMMV

But with that said... I've got Yellow Optimas in my personal unit.

Just struggling with ~$500 of batteries for a machine that sits idle 99% of the time.... especially when I see multiple posts regarding Optimas performing poorly. Not arguing... just saying... I'm struggling.

Got thinking. I owned a Chevy HHR until a few years ago when we traded it in for a VW Golf for our son. He'd driven the HHR all over the eastern seaboard and Canada. Had it for 9 years (9 winters), periods where it sat for 3 months w/o running or charging and finally, week before we decided to sell, the original ACDelco battery died. Got some aftermarket thing from advance auto, then sold the car.

I have heard similar stories about AC Delco's batteries from many other people.

Can't find it in a 51R format, closest is 47 AGM which is 9.5Lx6.9W and 6.9H with 630 CCA 60AH reserve. Amazon has 'em delivered for about $135. Optimas are 9.21L x 5W and 9tall and after having three of them die in less than 2 years' use, I wouldn't recommend them.

Don't have manual handy, anyone know the original size/format of the recommended batteries?

Thanks.

Confirming info - Group 51 =9.4L, 5.1W, and 8.8H. ....which is what lead to my original question as to whether the Group 35 would fit at 9.1, 6.9, 8.9. That width of ~1.8" is what I'm wondering about.

Thanks for all the info guys.