Truck running great. Driving for 100's of miles, no problem. Suddenly, unexpectedly..

[Jack Lope]

Just a follow up to the thread. Picked up the new/refurbished group 31 battery from Interstate and it was straight drop-in. I have to agree it looks like the battery trays were setup to use this size battery too. I only got one battery so still using the 6tmf as the second. Comparing the voltage and cranking amps, the new/refurbished battery was weaker slightly. After driving around a bit, both batteries seem to equalized at almost 13v and over 1000 CCA each on a meter held for about five seconds. Apparently, the old 6tmf battery that died had a bad cell.

 

[dependable]

I have found that if you mix a 31 (or any other standard lead acid battery) with a 6TMF, it will cause premature failure (usually to the 6TMF) due to different output and charging profiles of the two battery types. Matched pair is best.

The TMF stands for' 'thin metal film', and has some characteristics of a deep cycle battery.