Since we do have the Maxwell ESM (Engine Start Module ) we only had three batteries to test. My plan was, once the original batteries failed, to install true deep cycle batteries. The truck was originally equipped with "dual purpose" batteries. These batteries work well but the flaw in this design, as I see it, takes properties from a starting battery, which is cold cranking amps (CCA), to start these big diesel engines. Then it takes properties from a deep cycle battery, amp hours (AH), which is the ability to power accessories for long periods of
time. These properties are then combined into one battery, however these properties are polar opposites for their duties.
Once combined the result gives up the best of both designs. What does this mean to the battery owner? It means the battery will have fewer CCA's to start the engine, and fewer AH to run accessories, and a shorter life. In my experience, the typical auto battery will last about six years, the typical truck battery will last about eight months, we were right at 13 months. I do understand the loads on the batteries are completely different.
The truck engine is much harder to start and the auto doesn't sit for hours at a time, not running, providing power for its occupant to live comfortably.
This is the reason I wanted to install deep cycle batteries to replace the dual purpose batteries. Since there is no start load on the batteries we do not need the CCA's. We do sit for long periods so AH's is desired. Resulting in fewer low voltage starts of the generator.
Ok back to the battery shop. Once there, the batteries were disconnected and tested. HOLY COW, remember we only have three batteries, two were completely flat. Less than 50 CCA's in each, the third did not have even 350 CCA's, meaning the truck would NOT have started if we had to depend on the batteries.
Fortunately we do have the ESM and did not loose any loads because the truck wouldn't start. We have group 31 batteries and they do make a group 31 deep cycle battery, however, the deep cycle battery of choice only uses 5/16 stud
connections but also has a lead post. This created a problem, our cables are made for 3/8 stud connections and are specifically made to fit between the posts of the group 31 batteries in the battery box tray.
The lead posts of the replacement battery were in the way of connecting the batteries together. We could have built new cables using the lead posts or the smaller studs, but there was nothing wrong with the cables there. The battery shop didn't have the ability to build cables anyway. I didn't want to put the bad batteries back in the truck so we got the highest AH battery in a group 31 they had in stock. They seem to work fine and the generator doesn't start a lot for low voltage, for now. I have contacted a local battery supplier about getting a group 31 with 3/8 stud connections and no lead posts, they said no problem but they do not keep them in stock. I will let them know next time the generator starts more often than I think it should or when a test proves these batteries are failing to get three ordered.
So I didn't get to install the deep cycle batteries as planned, but I do know that they do make one to replace the group 31 that came in the truck. After these test results, it just proves the value of the Maxwell ESM. Who knows how much sooner we would have had to replace the batteries or if we would have lost a load and gotten a service failure because the truck wouldn't start.
Other ways to get the Maxwell ESM
Freightliner PDI Custom Truck Services. The selling dealer needs to contact the PDI center using http://www.freightliner-pdi.com/ to get a quote. The tricky part is, for a truck that is already built I would recommend using Maxwell’s recommended installers as the PDI center only installs on trucks recently released from the factory.