89 M998 Low Charge Indication

[Mogman]

Have you checked the connection on the opposite side of the + post that leaves the battery compartment? The 24V+ lead leaves the battery compartment in the front left corner by attaching to a post, not running the cable through the wall (at least in my HMMWV). That post has a 24V+ lead to the engine/starter/etc. on the outside terminal. I was having trouble like yours and kept checking connections for tightness, when I realized the 24V+ going out of the battery compartment just HAD to have a connection on the back of the post. It was indeed loose, and I've been worry free (more or less, it's a HMMWV) since I tightened it. One word of caution, you'll be tightening/checking a 24V+ nut about 2" from the starter body. Wrap that wrench to prevent grounding it out!
Hope this helps.
Bulldogger

You should disconnect the batteries before doing any electrical work.

 

[INFChief]

Roll your sleeves up a bit more and troubleshoot before throwing money at the problem.

My $0.02 is that the volt gauges on these vehicles are decent indicators but they aren’t calibrated units (unless something has changed since I was in). Checking for proper voltage at the batteries, NATO receptacle, and generator are the most accurate. Have you checked amperage at the batteries and at the generator?

As far as matched batteries unless your batteries are ancient I’ve never had a problem with replacing just 1 battery on any vehicle - providing the “good battery” tests out within the acceptable range for amperage, voltage, and draw.

Back to troubleshooting; First ask yourself “when did this problem surface? Had work been recently done on the vehicle when this popped up? Did you just return from a trip in it? What kind of equipment is installed? Is that equipment / accessories properly wired for it’s required power (12V or 24V)?”

It may sound goofy but verifying that the batteries are correctly installed and all connections are clean & tight is a great place to start.

Do you have access to any TM’s?

 

[Coug]

From what I've read/experienced over the years, when replacing a single battery in a multi-battery bank, you can expect the life of the replacement battery to be shortened to the same length as the rest of the batteries in the string. It might last longer, it might not. As long as all of the other batteries in the string are in good condition, you leave them alone.
I have yet to see a manufacturer or installer of batteries for battery banks to warranty an entire string of batteries for the failure of a single battery. It doesn't make any financial sense. The older batteries in the strong aren't going to be put under any more stress in a properly designed/maintained battery bank than the replacement simply because it's newer.
(yes, the manufacturer only cares about getting the batteries to last until the warranty expires, and it's cheaper to replace a single battery, or even several batteries in a larger strong than it is to replace all of them)

 

[TOBASH]

Guys, I respect you all but the short answer is to replace batteries as a matched set to maintain optimum lifespan.

Still, I look forward to watching as this debate rages on.

 

[Coug]

Guys, I respect you all but the short answer is to replace batteries as a matched set to maintain optimum lifespan.

Still, I look forward to watching as this debate rages on.

View attachment 868174

Yes, that is best practice, but not always the most economical.

With banks consisting of only 2 batteries, it does make more sense to replace as a pair, and even more so as they get older.

If they are still relatively new, then I might consider replacing only one, but the batteries I purchased for my truck have a full 5 year replacement warranty, so if one fails under warranty and the manufacturer does the replacement it's only going to be that battery; I won't pony up the hundreds of dollars for another battery until the warranty runs out. Manufacturer replacement under warranty doesn't start a new warranty, so I might only have a couple years or even a few months left for coverage on what's essentially a new battery.

Once warranty is over, then if a battery fails they'll get replaced as a pair and the battery of the two that's still good will get used in some other application around here, be it a vehicle/equipment or just as a utility battery when camping.

 

[15N AVI 998]

My apologies for the slow response, my schedule the last week has been all over the place. Yes, I did check the post as part of my contact cleaning. I was able to get all of the heavy points and a few of the smaller gauge connections from the batteries, to the starter, on up to the generator, and some of the start box connections. I'll refer to previous posts in this chain for voltage and amperage readings.

By the looks of things, I was able to recover the battery that went tengo uniform on me and is currently undergoing further conditioning.

As far as accessories are concerned, yes they are wired as needed, using step down voltage converters where required with all connections cleaned and tight. They aren't used all the time and are isolated by a contactor and circuit breakers/fuses. In regards to drive time, the vehicle is used as a daily driver with a few sporadic longer range trips from time to time.

I have downloaded several TMs and reference them often.